Phosphorescent materials

ABSTRACT

Novel organic compounds containing a twisted aryl group are provided. In particular, the compounds provided contain a 2-phenylpyridine ligand having a twisted aryl group on the pyridine portion of the ligand. The compounds may be used in organic light emitting devices, particularly as emitting dopants. Devices comprising the compounds containing twisted aryl may demonstrate improved color, efficiency, stability and manufacturing. Additionally, methods are provided for making homoleptic Ir (III) compounds which may contain a twisted aryl.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of the co-pending U.S.application Ser. No. 13/062,141 filed May 20, 2011, which is a U.S.national phase application filed under 35 U.S.C. §371 of InternationalApplication No. PCT/US2009/55890, filed Sep. 3, 2009, which is acontinuation-in-part of application No. PCT/US2009/052045, filed on Jul.29, 2009, claiming priority to provisional application No. 61/093,967,filed on Sep. 3, 2008, provisional application No. 61/140,459, filed onDec. 23, 2008, and provisional application No. 61/229,088, filed on Jul.28, 2009.

JOINT RESEARCH AGREEMENT

The claimed invention was made by, on behalf of, and/or in connectionwith one or more of the following parties to a joint universitycorporation research agreement: Regents of the University of Michigan,Princeton University, The University of Southern California, and theUniversal Display Corporation. The agreement was in effect on and beforethe date the claimed invention was made, and the claimed invention wasmade as a result of activities undertaken within the scope of theagreement.

FIELD OF THE INVENTION

The present invention relates to organic materials that may beadvantageously used in organic light emitting devices. Moreparticularly, the present invention relates to a method of makingorganic materials for such devices, as well as novel organic materials.

BACKGROUND

Opto-electronic devices that make use of organic materials are becomingincreasingly desirable for a number of reasons. Many of the materialsused to make such devices are relatively inexpensive, so organicopto-electronic devices have the potential for cost advantages overinorganic devices. In addition, the inherent properties of organicmaterials, such as their flexibility, may make them well suited forparticular applications such as fabrication on a flexible substrate.Examples of organic opto-electronic devices include organic lightemitting devices (OLEDs), organic phototransistors, organic photovoltaiccells, and organic photodetectors. For OLEDs, the organic materials mayhave performance advantages over conventional materials. For example,the wavelength at which an organic emissive layer emits light maygenerally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage isapplied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. Several OLED materials andconfigurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full colordisplay. Industry standards for such a display call for pixels adaptedto emit particular colors, referred to as “saturated” colors. Inparticular, these standards call for saturated red, green, and bluepixels. Color may be measured using CIE coordinates, which are wellknown to the art.

One example of a green emissive molecule is tris(2-phenylpyridine)iridium, denoted Ir(ppy)₃, which has the structure:

In this, and later figures herein, we depict the dative bond fromnitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as wellas small molecule organic materials that may be used to fabricateorganic opto-electronic devices. “Small molecule” refers to any organicmaterial that is not a polymer, and “small molecules” may actually bequite large. Small molecules may include repeat units in somecircumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be a fluorescent or phosphorescent smallmolecule emitter. A dendrimer may be a “small molecule,” and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules.

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. Where a first layer isdescribed as “disposed over” a second layer, the first layer is disposedfurther away from substrate. There may be other layers between the firstand second layer, unless it is specified that the first layer is “incontact with” the second layer. For example, a cathode may be describedas “disposed over” an anode, even though there are various organiclayers in between.

As used herein, “solution processable” means capable of being dissolved,dispersed, or transported in and/or deposited from a liquid medium,either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed thatthe ligand directly contributes to the photoactive properties of anemissive material. A ligand may be referred to as “ancillary” when it isbelieved that the ligand does not contribute to the photoactiveproperties of an emissive material, although an ancillary ligand mayalter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled inthe art, a first “Highest Occupied Molecular Orbital” (HOMO) or “LowestUnoccupied Molecular Orbital” (LUMO) energy level is “greater than” or“higher than” a second HOMO or LUMO energy level if the first energylevel is closer to the vacuum energy level. Since ionization potentials(IP) are measured as a negative energy relative to a vacuum level, ahigher HOMO energy level corresponds to an IP having a smaller absolutevalue (an IP that is less negative). Similarly, a higher LUMO energylevel corresponds to an electron affinity (EA) having a smaller absolutevalue (an EA that is less negative). On a conventional energy leveldiagram, with the vacuum level at the top, the LUMO energy level of amaterial is higher than the HOMO energy level of the same material. A“higher” HOMO or LUMO energy level appears closer to the top of such adiagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled inthe art, a first work function is “greater than” or “higher than” asecond work function if the first work function has a higher absolutevalue. Because work functions are generally measured as negative numbersrelative to vacuum level, this means that a “higher” work function ismore negative. On a conventional energy level diagram, with the vacuumlevel at the top, a “higher” work function is illustrated as furtheraway from the vacuum level in the downward direction. Thus, thedefinitions of HOMO and LUMO energy levels follow a different conventionthan work functions.

More details on OLEDs, and the definitions described above, can be foundin U.S. Pat. No. 7,279,704, which is incorporated herein by reference inits entirety.

SUMMARY OF THE INVENTION

A method is provided for making heteroleptic Ir(III) complexes havingextended conjugation. The method, comprising:

S is a neutral ligand. X is a counterion. Preferably, S is selected fromthe group consisting of triflate, tosylate, trifluoroacetate,tetrafluoroborate, and hexafluorophosphate. A and B are eachindependently a 5 or 6-membered aromatic or heteroaromatic ring, and A-Brepresents a bonded pair of aromatic or heteroaromatic rings coordinatedto the iridium via a nitrogen atom on ring A and an sp² hybridizedcarbon atom on ring B. C and D are each independently a 5 or 6-memberedaromatic or heteroaromatic ring, and C-D represents a bonded pair ofaromatic or heteroaromatic rings coordinated to the iridium via anitrogen ring atom on ring C and an sp² hybridized carbon atom on ringD. R_(A), R_(B), R_(C), and R_(D) are each independently selected fromthe group consisting of no substitution, alkyl, heteroalkyl, aryl, orheteroaryl groups. Each of R_(A), R_(B), R_(C), and R_(D) represent oneor more substituents. Preferably, R_(A), R_(B), R_(C), and R_(D) areselected from the group consisting of benzene, pyrimidine, pyridine,thiophene, thianapthene, fluorine, carbazole, and dibenzothiophene. R isan alkyl, heteroalkyl, or perfluoroalkyl group and the two Rs areoptionally joined to form a cycle.

Additionally, phosphorescent emissive materials are provided. Thematerials are heteroleptic complexes with extended conjugation on theheterocyclic ring. The materials may be advantageously used in organiclight emitting devices. In particular, the materials may be useful asthe emissive dopant of such devices. The materials are selected from thegroup consisting of:

In one aspect, Compound 1 may be preferred. In another aspect, Compound2 may be preferred.

Additionally, an organic light emitting device is provided. The devicehas an anode, a cathode, and an organic layer disposed between the anodeand the cathode, where the organic layer comprises a compound selectedfrom Compounds 1-6. The organic layer may further comprise a host.Preferably, the host includes a triphenylene group. More preferably, thehost includes a triphenylene further substituted with terphenyl. Mostpreferably, the host is H1.

A consumer product is also provided. The product contains a device thathas an anode, a cathode, and an organic layer disposed between the anodeand the cathode, where the organic layer further comprises a compoundselected from Compounds 1-6.

Heteroleptic iridium compounds are provided, which may be advantageouslyused in organic light emitting devices. The heteroleptic compounds areselected from the group consisting of:

In one aspect, Compound 8 may be preferred. In another aspect, Compound9 may be preferred. In yet another aspect, Compound 10 may be preferred.In a further aspect, Compound 11 may be preferred. In yet anotheraspect, Compound 12 may be preferred. In a further aspect, Compound 13may be preferred. In yet another aspect, Compound 14 may be preferred.

Additionally, an organic light emitting device is provided. The devicehas an anode, a cathode, and an organic layer disposed between the anodeand the cathode, where the organic layer comprises a compound selectedfrom Compounds 8-14. The organic layer may further comprise a hosthaving a triphenylene group further substituted with an aryl or aheteroaryl. Preferably, the host contains a triphenylene group furthersubstituted with a terphenyl or a dibenzothiophene. More preferably, thehost is H1 or H2.

A consumer product is also provided. The product contains a device thathas an anode, a cathode, and an organic layer disposed between the anodeand the cathode, where the organic layer further comprises a compoundselected from Compounds 8-14.

Additionally, a method for making heteroleptic compounds withoutsignificant ligand scrambling is provided. The method, comprising:

reacting

with

to form

S is a neutral ligand. X is a counterion. Preferably, X is selected fromthe group consisting of triflate, tosylate, trifluoroborate, andhexafluorophosphate. A and B are each independently a 5 or 6-memberedaromatic or heteroaromatic ring, and A-B represents a bonded pair ofaromatic or heteroaromatic rings coordinated to the iridium via anitrogen atom on ring A and an sp² hybridized carbon atom on ring B. Cand D are each independently a 5 or 6-membered aromatic orheteroaromatic ring, and C-D represents a bonded pair of aromatic orheteroaromatic rings coordinated to the iridium via a nitrogen ring atomon ring C and an sp² hybridized carbon atom on ring D. R_(A), R_(B),R_(C), and R_(D) are each independently selected from the groupconsisting of no substitution, alkyl, heteroalkyl, aryl, or heteroarylgroups, and each of R_(A), R_(B), R_(C), and R_(D) represent one or moresubstituents. Preferably, R_(A), R_(B), R_(C), and R_(D) are selectedfrom the group consisting of benzene, pyrimidine, pyridine, thiophene,thianaphthene, fluorine, carbazole, and dibenzothiophene. R_(Z) is notH. Preferably, R_(Z) is methyl.

A heteroleptic compound having the formula Ir(L_(A-B))₂(L_(C-D)) isprovided. L_(A-B) is

L_(C-D) is selected from the group consisting of

R₁, R₂, R₃, R₄ and R₅ are each independently selected from the groupconsisting of hydrogen and alkyl, and each of R₁, R₂, R₃, R₄ and R₅ mayrepresent mono, di, tri, tetra, or penta substitutions. Preferably, R₁,R₂, R₃, R₄ and R₅ are each independently hydrogen and methyl. Morepreferably, L_(C-D) is selected from the group consisting of:

Novel phosphorescent organic materials are provided. The organicmaterials are compounds containing at least one ligand having an alkylsubstituent and an aryl substituent such that the substituent aryl istwisted out of plane (i.e., twisted aryl in this document) more than theusual unsubstituted phenyl-phenyl. The compounds may be advantageouslyused in organic light emitting devices. In particular, the compounds maybe useful as an emitting dopant in such devices.

Compounds are provided, the compounds comprising a ligand L having thestructure:

B and C are each independently a 5 or 6-membered carbocyclic orheterocyclic ring. A-B represents a bonded pair of carbocyclic orheterocyclic rings coordinated to a metal M via a nitrogen atom on ringA and a sp² hybridized carbon atom on ring B. A-C represents a bondedpair of carbocyclic and heterocyclic rings. R_(a), R_(b), and R_(c) mayrepresent mono, di, tri, or tetra substitutions. R_(a), R_(b), and R_(c)are independently selected from the group consisting of hydrogen, alkyl,alkoxy, amino, alkenyl, alkynyl, arylkyl, aryl, and heteroaryl. X₁, X₂,X₃, X₄, X₅, X₆, X₇, X₈, and X₉ are independently selected from carbonand nitrogen. Preferably, A is pyridine. R₁ and R₂ are independentlyselected from the group consisting of hydrogen, alkyl, alkoxy, amino,alkenyl, alkynyl, arylkyl, aryl, and heteroaryl. At least one of R₁, R₂,and the R_(a) substituents adjacent to Ring C is not hydrogen.Preferably, only one of R₁, R₂, and the R_(a) substituents adjacent to Cis not hydrogen. Preferably, only one of R₁, R₂, and the R_(a)substituents adjacent to C is alkyl. More preferably, only one of R₁,R₂, and the R_(a) substituents adjacent to C is ethyl. Most preferably,only one of R₁, R₂, and the R_(a) substituents adjacent to C is methyl.The ligand L is coordinated to the metal M having an atomic numbergreater than 40. Preferably, the metal M is Ir.

Examples of the compounds may include compounds having the structure:

m is the oxidation state of the metal M. Preferably, the metal M is Ir.Preferably, A is pyridine. n is at least 1. L′ is a monoanionicbidentate ligand. Preferably, only one of R₁, R₂, and the R_(a)substituents adjacent to C is not hydrogen. Preferably, only one of R₁,R₂, and the R_(a) substituents adjacent to C is alkyl. More preferably,only one of R₁, R₂, and the R_(a) substituents adjacent to C is ethyl.Most preferably, only one of R₁, R₂, and the R_(a) substituents adjacentto C is methyl.

Particular examples of compounds having Formula II are provided andinclude Compound 15-Compound 20. R is not hydrogen. Preferably, R isalkyl.

Specific examples of compounds having Formula II are provided, includingCompound 21-Compound 37. In one aspect, Compounds 21, 22, 25, 29, 30, 31and 34 may be preferred compounds.

In one aspect, compounds are provided wherein the compound is selectedfrom the group consisting of:

At least one of R₁, R₂, R₃, and R₄ is not hydrogen. R₅ is selected fromthe group consisting of hydrogen, alkyl, alkoxy, amino, alkenyl,alkynyl, arylkyl, aryl, and heteroaryl. Preferably, A is pyridine. Inone aspect, R₁ and R₂ are hydrogen and one of R₃ and R₄ is alkyl.Exemplary compounds may include Compounds 21-24, 29-34, 36 and 37. Inanother aspect, one of R₁ and R₂ is alkyl and R₃ and R₄ are hydrogen.Exemplary compounds may include Compounds 25-28 and 35.

In another aspect, the compound is selected from the group consistingof:

Compounds having Formula II include homoleptic compounds andheteroleptic compounds. Examples of homoleptic compound includeCompounds 21-24 and 35. Examples of heteroleptic compounds includeCompounds 25-34, 36 and 37.

In one aspect, compounds are provided having a ligand L′ selected fromthe group consisting of:

R′₁, R′₂ and R′₃ are independently selected from the group consisting ofhydrogen, alkyl, alkoxy, amino, alkenyl, alkynyl, arylkyl, aryl, andheteroaryl.

In one aspect, compounds where the alkyl substituent (i.e., the alkylsubstituent inducing the twist in the aryl substituent) is present onthe pyridine ring of the ligand L are preferred. Preferably the compoundis selected from the group consisting of Compounds 21-23, 29-31, 34, 36and 37.

In another aspect, compounds where the alkyl substituent is para to thenitrogen of the pyridine ring may be especially preferred. Preferably,the compound is selected from the group consisting of Compounds 21, 22,29-31, 34, 36 and 37.

An organic light emitting device is also provided. The device has ananode, a cathode, and an organic layer disposed between the anode andthe cathode, where the organic layer comprises a compound having FormulaI, as described above. Selections for the substituents described aspreferred for the compounds having Formula I are also preferred for usein a device that comprises a compound having Formula I. These selectionsinclude those described for the metal M; the formulas II-VI; thesubstituents R, R₁, R₂, R₃, R₄, R₅, and R_(a) substituents adjacent toC; the position of ring C; and rings A, B, and C.

In one aspect, the device comprises a compound having Formula II, asdescribed above. Preferably, the metal M is Ir. Preferably, A ispyridine. In another aspect, the device comprises a compound havingFormula III or Formula IV, as described above. Devices containing acompound wherein only one of R₁, R₂, and the R_(a) substituents adjacentto C is alkyl may also be preferred. In yet another aspect, the devicecomprises a compound having Formula V or Formula VI, as described above.Certain devices are provided wherein the device contains a compoundselected from the group consisting of Compound 21-Compound 37.Preferably, the device contains Compound 21, Compound 22, Compound 25,Compound 29, Compound 30, Compound 31 or Compound 34.

In one aspect, devices are provided wherein the organic layer is anemissive layer and the compound having the formula of Formula I is anemitting dopant. Moreover, the organic layer may further comprise ahost. Preferably, the host has the structure:

R′₁, R′₂, R′₃, R′₄, R′₅, and R′₆ are independently selected from thegroup consisting of hydrogen, alkyl, alkoxy, amino, alkenyl, alkynyl,arylkyl, aryl, and heteroaryl.

A consumer product comprising a device is also provided. The devicecomprises an anode, a cathode, and an organic layer disposed between theanode and the cathode, where the organic layer comprises a compoundhaving Formula I, as described above. Selections for the substituentsdescribed as preferred for the compounds having Formula I are alsopreferred for use in a consumer product containing a device thatcomprises a compound having Formula I. These selections include thosedescribed for the metal M; the formulas II-VI; the substituents R, R₁,R₂, R₃, R₄, R₅, and R_(a) substituents adjacent to C; the position ofring C; and rings A, B, and C.

Additionally, low temperature methods for making homoleptic compoundsare provided. In particular, the methods are for making homoleptic Ir(III) compounds. These compounds may preferably contain a twisted aryl.

A first method for making a homoleptic Ir(III) complex is provided. Thefirst method comprising:

reacting

with

in the presence of a low boiling alcohol to form

At least one of R_(A) and R_(B) is an alkyl group and the alkyl group isnot adjacent to the nitrogen on the pyridine ring. S is a neutralligand. X is a counterion. Preferably, X is triflate. A and B are eachindependently a 5 or 6-membered carbocyclic or heterocyclic ring. A-Brepresents a bonded pair of carbocyclic or heterocyclic ringscoordinated to the iridium via a nitrogen atom on ring A and an sp²hybridized carbon atom on ring B. Each of R_(A) and R_(B) may representmono, di, tri, or tetra substitutions. R_(A) and R_(B) are eachindependently selected from the group consisting of hydrogen, alkyl,alkoxy, amino, alkenyl, alkynyl, arylkyl, aryl, and heteroaryl.

In one aspect, the low boiling alcohol is selected from the groupconsisting of methanol, ethanol, n-propanol, isopropanol, n-butanol, a1:1 ratio of ethanol and methanol, 2-methoxyethanol, and2-ethoxyethanol. Preferably, the low boiling alcohol is selected fromthe group consisting of isopropanol which boils at 108° C., ethanolwhich boils at 78° C., and a 1:1 ratio of ethanol and methanol which hasa boiling point between 65° C. and 78° C. More preferably, the lowboiling alcohol is ethanol or a 1:1 ratio of ethanol and methanol. Mostpreferably, the low boiling alcohol is a 1:1 ratio of ethanol andmethanol.

Preferably, A is:

C is a 5 or 6-membered carbocyclic or heterocyclic ring. A-C representsa bonded pair of carbocyclic and heterocyclic rings. R_(A) and R_(C) mayrepresent mono, di, tri, or tetra substitutions. R_(A) and R_(C) areindependently selected from the group consisting of hydrogen, alkyl,alkoxy, amino, alkenyl, alkynyl, arylkyl, aryl, and heteroaryl. X₁, X₂,X₃, X₄, X₅, X₆, X₇, X₈, and X₉ are independently selected from carbonand nitrogen. R₁ and R₂ are independently selected from the groupconsisting of hydrogen, alkyl, alkoxy, amino, alkenyl, alkynyl, arylkyl,aryl, and heteroaryl. At least one of R₁, R₂, and the R_(a) substituentsadjacent to C is not hydrogen.

In one aspect, the first method comprises:

reacting

with

in the presence of a low boiling alcohol to form

Specific compounds, including Compound 21, Compound 22, and Compound 24,may be formed using this method.

A second method for making homoleptic Ir (III) compounds is alsoprovided. The second method comprises:

reacting

with

in the absence of solvent to form

At least one of R_(A) and R_(B) is an alkyl group and the alkyl group isadjacent to the nitrogen on the pyridine ring. S is a neutral ligand. Xis a counterion. Preferably, X is triflate. A and B are eachindependently a 5 or 6-membered carbocyclic or heterocyclic ring. A-Brepresents a bonded pair of carbocyclic or heterocyclic ringscoordinated to the iridium via a nitrogen atom on ring A and an sp²hybridized carbon atom on ring B. Each of R_(A) and R_(B) may representmono, di, tri, or tetra substitutions. R_(A) and R_(B) are eachindependently selected from the group consisting of hydrogen, alkyl,alkoxy, amino, alkenyl, alkynyl, arylkyl, aryl, and heteroaryl.

Preferably, A is:

C is a 5 or 6-membered carbocyclic or heterocyclic ring. A-C representsa bonded pair of carbocyclic and heterocyclic rings. R_(A) and R_(C) mayrepresent mono, di, tri, or tetra substitutions. R_(A) and R_(C) areindependently selected from the group consisting of hydrogen, alkyl,alkoxy, amino, alkenyl, alkynyl, arylkyl, aryl, and heteroaryl. X₁, X₂,X₃, X₄, X₅, X₆, X₇, X₈, and X₉ are independently selected from carbonand nitrogen. R₁ and R₂ are independently selected from the groupconsisting of hydrogen, alkyl, alkoxy, amino, alkenyl, alkynyl, arylkyl,aryl, and heteroaryl. At least one of R₁, R₂, and the R_(a) substituentsadjacent to C is not hydrogen.

In one aspect, the second method comprises:

reacting

with

in the absence of solvent to form

Specific compounds, including Compound 23, may be formed using thismethod.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does nothave a separate electron transport layer.

FIG. 3 shows a PHOLED having a particular structure.

FIG. 4 shows a method of making heteroleptic Ir (III) compounds.

FIG. 5 shows heteroleptic Ir (III) complexes having extendedconjugation.

FIG. 6 shows a method for making heteroleptic Ir (III) compounds.

FIG. 7 shows a ligand containing a twisted aryl and a compoundcomprising a ligand containing a twisted aryl.

FIG. 8 shows exemplary compounds.

FIG. 9 shows a method for making homoleptic Ir (III) compounds.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed betweenand electrically connected to an anode and a cathode. When a current isapplied, the anode injects holes and the cathode injects electrons intothe organic layer(s). The injected holes and electrons each migratetoward the oppositely charged electrode. When an electron and holelocalize on the same molecule, an “exciton,” which is a localizedelectron-hole pair having an excited energy state, is formed. Light isemitted when the exciton relaxes via a photoemissive mechanism. In somecases, the exciton may be localized on an excimer or an exciplex.Non-radiative mechanisms, such as thermal relaxation, may also occur,but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from theirsinglet states (“fluorescence”) as disclosed, for example, in U.S. Pat.No. 4,769,292, which is incorporated by reference in its entirety.Fluorescent emission generally occurs in a time frame of less than 10nanoseconds.

More recently, OLEDs having emissive materials that emit light fromtriplet states (“phosphorescence”) have been demonstrated. Baldo et al.,“Highly Efficient Phosphorescent Emission from OrganicElectroluminescent Devices,” Nature, vol. 395, 151-154, 1998;(“Baldo-I”) and Baldo et al., “Very high-efficiency green organiclight-emitting devices based on electrophosphorescence,” Appl. Phys.Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), which are incorporatedby reference in their entireties. Phosphorescence is described in moredetail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporatedby reference.

FIG. 1 shows an organic light emitting device 100. The figures are notnecessarily drawn to scale. Device 100 may include a substrate 110, ananode 115, a hole injection layer 120, a hole transport layer 125, anelectron blocking layer 130, an emissive layer 135, a hole blockinglayer 140, an electron transport layer 145, an electron injection layer150, a protective layer 155, and a cathode 160. Cathode 160 is acompound cathode having a first conductive layer 162 and a secondconductive layer 164. Device 100 may be fabricated by depositing thelayers described, in order. The properties and functions of thesevarious layers, as well as example materials, are described in moredetail in U.S. Pat. No. 7,279,704 at cols. 6-10, which are incorporatedby reference.

More examples for each of these layers are available. For example, aflexible and transparent substrate-anode combination is disclosed inU.S. Pat. No. 5,844,363, which is incorporated by reference in itsentirety. An example of a p-doped hole transport layer is m-MTDATA dopedwith F.sub.4-TCNQ at a molar ratio of 50:1, as disclosed in U.S. PatentApplication Publication No. 2003/0230980, which is incorporated byreference in its entirety. Examples of emissive and host materials aredisclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which isincorporated by reference in its entirety. An example of an n-dopedelectron transport layer is BPhen doped with Li at a molar ratio of 1:1,as disclosed in U.S. Patent Application Publication No. 2003/0230980,which is incorporated by reference in its entirety. U.S. Pat. Nos.5,703,436 and 5,707,745, which are incorporated by reference in theirentireties, disclose examples of cathodes including compound cathodeshaving a thin layer of metal such as Mg:Ag with an overlyingtransparent, electrically-conductive, sputter-deposited ITO layer. Thetheory and use of blocking layers is described in more detail in U.S.Pat. No. 6,097,147 and U.S. Patent Application Publication No.2003/0230980, which are incorporated by reference in their entireties.Examples of injection layers are provided in U.S. Patent ApplicationPublication No. 2004/0174116, which is incorporated by reference in itsentirety. A description of protective layers may be found in U.S. PatentApplication Publication No. 2004/0174116, which is incorporated byreference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210,a cathode 215, an emissive layer 220, a hole transport layer 225, and ananode 230. Device 200 may be fabricated by depositing the layersdescribed, in order. Because the most common OLED configuration has acathode disposed over the anode, and device 200 has cathode 215 disposedunder anode 230, device 200 may be referred to as an “inverted” OLED.Materials similar to those described with respect to device 100 may beused in the corresponding layers of device 200. FIG. 2 provides oneexample of how some layers may be omitted from the structure of device100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided byway of non-limiting example, and it is understood that embodiments ofthe invention may be used in connection with a wide variety of otherstructures. The specific materials and structures described areexemplary in nature, and other materials and structures may be used.Functional OLEDs may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be strictly limiting. For example, in device 200, holetransport layer 225 transports holes and injects holes into emissivelayer 220, and may be described as a hole transport layer or a holeinjection layer. In one embodiment, an OLED may be described as havingan “organic layer” disposed between a cathode and an anode. This organiclayer may comprise a single layer, or may further comprise multiplelayers of different organic materials as described, for example, withrespect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used,such as OLEDs comprised of polymeric materials (PLEDs) such as disclosedin U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated byreference in its entirety. By way of further example, OLEDs having asingle organic layer may be used. OLEDs may be stacked, for example asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated by reference in its entirety. The OLED structure maydeviate from the simple layered structure illustrated in FIGS. 1 and 2.For example, the substrate may include an angled reflective surface toimprove out-coupling, such as a mesa structure as described in U.S. Pat.No. 6,091,195 to Forrest et al., and/or a pit structure as described inU.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated byreference in their entireties.

Unless otherwise specified, any of the layers of the various embodimentsmay be deposited by any suitable method. For the organic layers,preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. patent application Ser. No. 10/233,470, which is incorporated byreference in its entirety. Other suitable deposition methods includespin coating and other solution based processes. Solution basedprocesses are preferably carried out in nitrogen or an inert atmosphere.For the other layers, preferred methods include thermal evaporation.Preferred patterning methods include deposition through a mask, coldwelding such as described in U.S. Pat. Nos. 6,294,398 and 6,468,819,which are incorporated by reference in their entireties, and patterningassociated with some of the deposition methods such as ink-jet and OVJD.Other methods may also be used. The materials to be deposited may bemodified to make them compatible with a particular deposition method.For example, substituents such as alkyl and aryl groups, branched orunbranched, and preferably containing at least 3 carbons, may be used insmall molecules to enhance their ability to undergo solution processing.Substituents having 20 carbons or more may be used, and 3-20 carbons isa preferred range. Materials with asymmetric structures may have bettersolution processibility than those having symmetric structures, becauseasymmetric materials may have a lower tendency to recrystallize.Dendrimer substituents may be used to enhance the ability of smallmolecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the invention maybe incorporated into a wide variety of consumer products, including flatpanel displays, computer monitors, televisions, billboards, lights forinterior or exterior illumination and/or signaling, heads up displays,fully transparent displays, flexible displays, laser printers,telephones, cell phones, personal digital assistants (PDAs), laptopcomputers, digital cameras, camcorders, viewfinders, micro-displays,vehicles, a large area wall, theater or stadium screen, or a sign.Various control mechanisms may be used to control devices fabricated inaccordance with the present invention, including passive matrix andactive matrix. Many of the devices are intended for use in a temperaturerange comfortable to humans, such as 18 degrees C. to 30 degrees C., andmore preferably at room temperature (20-25 degrees C.).

The materials and structures described herein may have applications indevices other than OLEDs. For example, other optoelectronic devices suchas organic solar cells and organic photodetectors may employ thematerials and structures. More generally, organic devices, such asorganic transistors, may employ the materials and structures.

The terms halo, halogen, alkyl, cycloalkyl, alkenyl, alkynyl, arylkyl,heterocyclic group, aryl, aromatic group, and heteroaryl are known tothe art, and are defined in U.S. Pat. No. 7,279,704 at cols. 31-32,which are incorporated herein by reference.

Compounds are provided, comprising a heteroleptic Ir (III) complexhaving extended conjugation. In particular, the complex has extendedconjugation on the heterocyclic ring which coordinates to the metalthrough nitrogen. Heteroleptic iridium complexes are of great interestbecause their photophysical, thermal, and electronic properties can betuned according to the ligands that are attached to the metal center.One advantage to using heteroleptic iridium complexes is that they offerimproved device lifetime and a lower sublimation temperature, thereforeoffering improved manufacturing, as compared to homoleptic Ir (III)complexes. For example, a heteroleptic complex containing2-phenylpyridine and 2-(biphenyl-3-yl)pyridine, has shown an improvedlifetime compared to a related homoleptic complex. Further, thesublimation temperature of the heteroleptic complex is almost 70° C.lower than the homoleptic complex. See, U.S. Provisional Application No.60/940,310. Heteroleptic complexes which demonstrate improved stabilityand low sublimation temperatures, such as those disclosed herein, arehighly desirable for use in OLEDs. In particular, the heteroleptic Ir(III) complexes may be especially desirable for use in white organiclight emitting devices (WOLEDs).

The existing synthetic methods for making many heteroleptic iridiumcomplexes may not be practical. In particular, existing synthetic routesinclude the halogenation of iridium complexes and further functionalized(see, Stossel et al., Rhodium complexes and iridium complexes, 2005,EP1504015B1; Stossel et al., Rhodium and iridium complexes, 2006, U.S.Pat. No. 7,125,998), the use of boronic ester substituted iridiumcomplexes generated from halogenated complexes and furtherfunctionalized (see, Kwong et al., Method for synthesis of iridium (III)complexes with sterically demanding ligands, 2006, U.S. application Ser.No. 12/044,848), and the low temperature BuLi/ZnCl₂ method (see, Huo etal, OLEDs with mixed ligand cyclometallated complexes, 2006,US20060134459A1). The low temperature BuLi/ZnCl₂ method, for example,produces mer-isomers of the complex, which are not normally desired, andthus must then be converted to the useful fac-isomer of the complex.See, Huo et al, OLEDs with mixed ligand cyclometallated complexes, 2006,US20060134459A1. Thus, this method may not be practical for large scalesynthesis of the complex. While offering improved yield, the method thatinvolves converting a brominated iridium complex to a boronic ester toultimately yield the final product is indirect. See, Kwong et al.,Method for synthesis of iridium (III) complexes with stericallydemanding ligands, 2006, U.S. application Ser. No. 12/044,848.Therefore, it is highly desirable to provide a more practical and directsynthetic method for making heteroleptic Ir (III) complexes.

The method, as described herein, can be used to make heteroleptic Ir(III) complexes that may be advantageously used in OLEDs and, inparticular, WOLEDs. For example, the method described herein can be usedto make especially desirable heteroleptic Ir (III) complexes such asCompound 1, Compound 2 and Compound 7.

A method for making Ir (III) heteroleptic complexes having extendedconjugation, the method comprising

reacting

with

to form

where S is a neutral ligand. X is a counterion. A and B are eachindependently a 5 or 6-membered aromatic or heteroaromatic ring, and A-Brepresents a bonded pair of aromatic or heteroaromatic rings coordinatedto the iridium via a nitrogen atom on ring A and an sp² hybridizedcarbon atom on ring B. C and D are each independently a 5 or 6-memberedaromatic or heteroaromatic ring, and C-D represents a bonded pair ofaromatic or heteroaromatic rings coordinated to the iridium via anitrogen ring atom on ring C and an sp² hybridized carbon atom on ringD. R_(A), R_(B), R_(C), and R_(D) are each independently selected fromthe group consisting of no substitution, alkyl, heteroalkyl, aryl, orheteroaryl groups. Each of R_(A), R_(B), R_(C), and R_(D) represent oneor more substituents. R is an alkyl, heteroalkyl, or perfluoroalkylgroup and the two Rs are optionally joined to form a cycle.

In one aspect of the method, the counterion X is selected from the groupconsisting of triflate, tosylate, trifluoroacetate, tetrafluoroborate,and hexafluorophosphate.

In one aspect, R_(A), R_(B), R_(C), and R_(D) are selected from thegroup consisting of benzene, pyrimidine, pyridine, thiophene,thianaphthene, fluorine, carbazole, and dibenzothiophene.

In another aspect, the method includes

reacting

with

to form

In one aspect of the method, the group B(OR)₂ is attached to ring C. Inanother aspect, the group B(OR)₂ is attached to ring D. In a particularaspect of the method, the group B(OR)₂ is

In one aspect, the method includes

reacting

with RX to form

wherein R is aryl or heteroaryl and X is selected from the groupconsisting of I, Br, Cl, and OTf.

In one aspect, the method includes

reacting

with

to form

In a certain aspect of the method, the complex

is

In another aspect, the complex is

In yet another aspect, the complex is

In another aspect, the method includes

reacting

with

to form

In a certain aspect of the method, the complex

is

In another aspect, the method includes

reacting

with

to form

In a certain aspect, the complex

is

In another aspect, the method includes

reacting

with

to form

In a certain aspect, the complex

is

In yet another aspect, the method includes

reacting

with

to form

In a certain aspect of the method, the complex

is

In another aspect, the method further includes

reacting

with

to form

and reacting

with AgX to form

and then reacting

with

to form

Additionally, phosphorescent emissive compounds are provided. Inparticular, the compounds are Ir (III) heteroleptic complexes havingextended conjugation on the heterocyclic ring which coordinates to themetal through nitrogen. The compounds provided have the formula selectedfrom the group consisting of:

Certain compounds may be particularly beneficial. In one aspect,preferably the compound is Compound 1. In another aspect, preferably thecompound is Compound 2.

Heteroleptic iridium compounds are provided, which may be advantageouslyused in organic light emitting devices. In particular, the compounds maybe useful as the emissive dopant of such devices. The heterolepticcompounds are selected from the group consisting of:

Certain compounds may be particularly beneficial. In one aspect,preferably the compound is Compound 8. In another aspect, preferably thecompound is Compound 9. In yet another aspect, preferably the compoundis Compound 10. In a further aspect, preferably the compound is Compound11. In yet another aspect, preferably the compound is Compound 12. In afurther aspect, preferably the compound is Compound 13. In yet anotheraspect, preferably the compound is Compound 14.

Additionally, an organic light emitting device is provided, the devicecomprising an anode, a cathode, and an organic layer disposed betweenthe anode and the cathode, and the organic layer further comprising acompound selected from the group consisting of:

In one aspect, the organic layer of the device further comprises a host.Compounds 1 and 2 have been shown to work particularly well in deviceshaving a host that contains a triphenylene group. In particular, thesecompounds are advantageously used in devices wherein the host has theformula

R is aryl or heteroaryl. In a certain aspect, the host compound has theformula where R is terphenyl. Moreover, the inventive compounds may beespecially useful in a device wherein the host has the structure

An organic light emitting device is provided, the device comprising ananode, a cathode, and an organic layer disposed between the anode andthe cathode. The organic layer further comprises a compound selectedfrom the group consisting of:

The organic layer of the device may further comprise a host. Compounds7-12 have been shown to work particularly well in devices having a hostthat contains a triphenylene group. In particular, the compounds may beused in a device wherein the host has the formula

where R is aryl or heteroaryl. In one aspect, the host compound has theformula described above where R is terphenyl. Preferably, the compoundsmay be used in a device wherein the host has the structure

In another aspect, the compounds may be used in a device wherein thehost has the formula described above where R is dibenzothiophene.Preferably, the compounds may be used in a device wherein the host hasthe structure

Additionally, a consumer product comprising the device is also provided.The device further comprises an anode, a cathode, and an organic layerdisposed between the anode and the cathode. The organic layer contains acompound selected from Compounds 1-6.

A consumer product comprising a device is also provided, wherein thedevice further comprises an anode, a cathode and an organic layer whichis disposed between the anode and the cathode. The organic layer furthercomprises a compound selected from the group consisting of Compounds8-14.

As discussed previously, the existing synthetic methods for makingheteroleptic iridium complexes may not be practical for the productionof many compounds. One commonly used synthetic route involves reactingan iridium triflate intermediate with a second ligand in an organicsolvent to produce heteroleptic iridium complexes.

However, this method often produces a mixture of products because of theligand scrambling during the reaction. Specifically, this methodgenerates both major and minor products in varying yields. The mixtureof product compounds can cause problems in purifying the desired productand therefore may limit the practicality of the synthesis.

Of note, several of the heteroleptic iridium compounds provided herein(i.e., Compounds 10, 11 and 14) were generated in high yield and withouta significant amount of contaminating minor products using a triflateintermediate synthesis when an alkyl-substituted triflate intermediate(e.g., 6′-methylphenylpyridine) was used. The very low degree of ligandscrambling in the synthesis of Compounds 10, 11 and 14 was unexpected atleast in part because the same synthesis failed to provide the sameresults when used to make other compounds structurally similar toCompound 11 (e.g., Compound 2). See Example 8 and Experimental Section.

Accordingly, a method for making heteroleptic compounds having extendedconjugation is provided herein (illustrated in FIG. 6). The methodcomprises reacting

with

to form

S is a neutral ligand. X is a counterion. A and B are each independentlya 5 or 6-membered aromatic or heteroaromatic ring, and A-B represents abonded pair of aromatic or heteroaromatic rings coordinated to theiridium via a nitrogen atom on ring A and an sp² hybridized carbon atomon ring B. C and D are each independently a 5 or 6-membered aromatic orheteroaromatic ring, and C-D represents a bonded pair of aromatic orheteroaromatic rings coordinated to the iridium via a nitrogen ring atomon ring C and an sp² hybridized carbon atom on ring D. R_(A), R_(B),R_(C), and R_(D) are each independently selected from the groupconsisting of no substitution, alkyl, heteroalkyl, aryl, or heteroarylgroups, and each of R_(A), R_(B), R_(C), and R_(D) represent one or moresubstituents. R_(Z) is not H.

Preferably, the counterion X is selected from the group consisting oftriflate, tosylate, trifluoroborate, and hexafluorophosphate.

R_(A), R_(B), R_(C), and R_(D) are preferably selected from the groupconsisting of benzene, pyrimidine, pyridine, thiophene, thianaphthene,fluorine, carbazole, and dibenzothiophene. Additionally, R_(Z) ispreferably an alkyl and more preferably R_(Z) is methyl.

In one aspect, the method includes

reacting

with

to form

Preferably,

is selected from the group consisting

The method comprises an alkyl substituted-phenylpyridine (e.g.,6-methylphenylpyridine), instead of phenylpyridine, as the A-B ligandwhich when reacted with the C-D ligand may result in no significantscrambling of the reaction products thereby providing an easier topurify product. In particular, the method described above was used tosynthesize Compounds 10, 11 and 14 and demonstrated high yield of thedesired product with very low contamination with scrambled product.After the reaction was complete, the reaction product was analyzedchromatographically. Specifically, HPLC percentages of the major productfor Compounds 10, 11, and 14 were calculated as 99.4%, 99.4 and 99.4%,respectively, whereas the minor products have combined HPLC percentagesof 0.3%, 0.5%, and 0.5%, respectively, in the unpurified precipitatedproduct. On the other hand, if the existing triflate intermediate methodwas used to make heteroleptic compounds, i.e., the 6-position of L_(A-B)is not substituted, significant scrambling of the product can occur. Inparticular, synthesis of Compounds 2 and 7 using the existing methodprovided 92% and 91% respectively of the major product, and 8% and 9%respectively of the minor products in the unpurified reaction mixture(as determined by HPLC). Thus, the method using alkylsubstituted-phenylpyridine ligands described above provide an improvedsynthesis for heteroleptic compounds.

Additionally, heteroleptic compounds having the formulaIr(L_(A-B))₂(L_(C-D)) are provided. L_(A-B) is

L_(C-D) is selected from the group consisting of:

R₁, R₂, R₃, R₄ and R₅ are each independently selected from the groupconsisting of hydrogen and alkyl, and each of R₁, R₂, R₃, R₄ and R₅ mayrepresent mono, di, tri, tetra, or penta substitutions. Preferably, R₁,R₂, R₃, R₄ and R₅ are each independently selected from hydrogen andmethyl.

The ligand L_(C-D) is preferably selected from the group consisting of:

2-Phenylpyridine and alkyl substituted 2-phenylpyridine ligands mayprovide beneficial properties. In particular, these ligands bindstrongly with iridium (III). Thus, 2-phenylpyridine and alkylsubstituted 2-phenylpyridine provide good chemical stability.Additionally, the tris complexes of iridium and 2-phenylpyridine ligandsevaporate under high vacuum at low temperatures (i.e., <250° C.).However, the operational stability of PHOLEDs using these complexes asemitters is poor and thus needs to be improved. Aryl substitution on2-phenylpyridine can improve device stability. Unfortunately, the trisiridium complexes of aryl substituted 2-phenylpyridine can only beevaporated at high temperatures (i.e., >290° C.). High evaporationtemperature is not desirable for long term manufacturing due todecomposition. Therefore, the use of such tris aryl substituted2-phenylpyridine in PHOLEDs may be limited. The heteroleptic compoundsprovided herein comprise two non-substituted 2-phenylpyridine ligands oralkyl substituted 2-phenylpyridine ligands, and one aryl substituted2-phenylpyridine ligand. Thus, the heteroleptic compounds providedherein may provide lower evaporation temperature and improve deviceoperational lifetime.

In particular, compound 7, which has two 2-phenylpyridine ligands andone 2-(biphenyl-3-yl)pyridine ligand, demonstrated improved stability ina PHOLED compared with tris(2-phenylpyridine)iridium(III). The emissionspectrum of compound 7 was slightly red shifted. However, the emissionwas blue shifted in comparison totris(2-(biphenyl-3-yl)pyridine)iridium(III). Taken together, thissuggests that both ligands, i.e., 2-phenylpyridine and2-(biphenyl-3-yl)pyridine, probably contributed to the emission. Inaddition, the oxidation and reduction properties of compound 7,tris(2-phenylpyridine)iridium(III), andtris(2-(biphenyl-3-yl)pyridine)iridium(III) were measured by cyclicvoltammetry and there was no significant difference between the valuesfor the three different compounds. Therefore, the substitution patternof the compound may not significantly shift the HOMO and LUMO levels ofthe complexes.

For the heteroleptic compounds Ir(L_(A-B))₂(L_(C-D)) provided herein,the combination of the ligand L_(C-D) with the ligand L_(A-B) providedbetter conjugation to the pyridine ring, where the LUMO locates. Withoutbeing bound by theory, it is thought that the LUMO of the providedheteroleptic compounds was reduced significantly as a result of theconjugation and stabilized the pyridine ring. At the same time, theemission spectrum became almost identical to Ir(L_(C-D))₃, i.e.,tris(2-phenylpyridine)iridium (III) with aryl on the pyridine,suggesting that the emission is dominated by L_(C-D) while L_(A-B) is anon-emitting ligand. The heteroleptic compounds Ir(L_(A-B))₂(L_(C-D))disclosed herein provide high device stability. For the heterolepticcompounds Ir(L_(A-B))(L_(C-D))₂ provided herein, the effect is similar.

As discussed in previous paragraphs, the synthesis of heteroleptic Ir(III) complexes may be improved by a method wherein a boronic esterfunctionalized ester is reacted directly with an iridium complexintermediate. The method is also shown in FIG. 4. In particular, thesynthesis may be more practical for large scale synthesis of thecomplexes. The products of the reaction can be separated by column orother methods. In addition, heteroleptic Ir (III) complexes havingextended conjugation from the heterocyclic ring may be made according tothe method described herein. These compounds are also shown in FIG. 5.The use of these complexes in devices may result in improved devicestability and manufacturing.

As discussed above, the synthesis of heteroleptic Ir (III) compounds maybe improved by a method wherein a substituted triflate iridiumintermediate is reacted with a second ligand. The method is also shownin FIG. 6. In particular, the synthesis may provide improved productpurification due to significantly reduced ligand scrambling.

Novel compounds are provided, the compounds comprise at least one ligandcontaining a twisted aryl (illustrated in FIG. 7). Specific compoundsprovided include Ir(2-phenylpyridine)type compounds containing a twistedphenyl ring (illustrated in FIG. 8). These twisted aryl compounds may beadvantageously used in OLEDs to provide devices having improvedefficiency, stability and manufacturing. Preferably, these compounds maybe used as an emitting dopant in such devices.

Compounds containing a twisted aryl group have been reported in theliterature (see, e.g., US2007/0003789 and US2009/0124805).

While 2-phenylpyridine and alkyl substituted 2-phenylpyridine ligandsform iridium(III) compounds with good properties, these compounds mayhave limited practical use in devices (e.g., poor operationalstability). Aryl substitution on 2-phenylpyridine can improve deviceefficiency, but tris iridium compounds of aryl substituted2-phenylpyridine can only be evaporated at high temperatures (i.e.,above 290° C.) thereby limiting the use of these compounds as well(i.e., decomposition in manufacturing). It was found that2-phenylpyridine type ligands having particular substitution patternsmay be particularly beneficial. In particular, the strategic combinationof alkyl and phenyl substitutions on the 2-phenylpyridine type ligandmay result in the substituent aryl group twisting out of plane (i.e.,twisted aryl) thereby reducing packing and lowering the evaporationtemperature. The compounds provided herein comprise at least one ligandwith an alkyl and aryl substituent such that the substituent aryl is atwisted aryl. Thus, these compounds may provide lower evaporationtemperature, improve device manufacturing and improve device operationallifetime.

Aryl groups substituted on 2-phenylpyridine may also increase theconjugation of the ligand thereby resulting in a red shifted emission.Such compounds having emission at longer wavelengths in the yellow partof the spectrum, such as 540 nm to 580 nm, may have limited use becausethere emission is limited to the yellow part of the spectrum. Therefore,compounds having emission at a different range, such as a blue shiftedrange, may be desirable. In particular, compounds with an emission inthe target energy range of about 521 nm to about 540 nm may beparticularly desirable. It is believed that compounds in which thesubstituent aryl ring is twisted by the addition of an alkyl group mayhave limited conjugation and demonstrate a blue shifted emission. Inparticular, the twisted aryl compounds provided herein may have emissionenergies that are blue shifted relative to the corresponding compoundscontaining untwisted aryl substituents. Therefore, these blue shiftedcompounds may be particularly preferable.

Compounds containing at least one ligand with a twisted aryl areprovided. The effect of different twisted aryl substitution patterns onthe emissive ligand was studied to establish a structure-propertyrelationship for substituted Ir(2-phenylpyridine) type phosphorescentmaterials and devices containing such materials. Several aspects ofmaterial processibility, including evaporation temperature, evaporationstability, and solubility, as well as device characteristics of PHOLEDsusing twisted phenyl containing compounds were studied. Strategicallypositioned substituents present on the compound may lead to the twistingof the substituent aryl ring. For example, substituents present on thearyl group (i.e., ring C) or on the pyridine ring adjacent to thetwisted aryl (i.e., ring A) may induce the extra twisting of the arylgroup. As a result, the compounds having a twisted aryl moiety mayprovide (i) reduced conjugation thereby minimizing the red-shiftingeffect that is usually associated with increased conjugation (i.e., theadditional of a phenyl), (ii) reduced stacking thereby loweringevaporation temperatures and increasing long-term thermal stability andprocessability, and (iii) narrow emission thus resulting in highluminous efficiency (i.e., high LE:EQE).

Compounds containing a twisted aryl and a limited number of substituents(e.g., a single substituent) may provide improved stability whilemaintaining the benefits of the twisted aryl, such as improvedefficiency and manufacturing. Further, certain compounds provided hereinmay demonstrate particularly narrow emission thus providing deviceshaving especially good luminous efficiency in addition to the othernoted improvements. Therefore, the compounds provided herein may beparticularly desirable.

Without being bound by theory, it is believed that compounds having onlyone substituent inducing the twist in the substituent aryl may beespecially beneficial. In particular, compounds with a singlesubstituent inducing the twist of the aryl substituent may be morestable than corresponding compounds containing multiple substituents. Itis thought that compounds having a single substituent may have a smallerdegree of twisting between the substituent aryl and the remainder of theligand, and thus more conjugation, as compared to compounds withmultiple substituents which may have a higher degree of twisting out ofplane. Specifically, it is thought that compounds with a single methylsubstituent may have improved stability compared to compounds havingmultiple methyl substituents. For example, Device Example 28 andComparative Device Example 6 have the same device structure andcomposition except that Device Example 28 uses Compound 35 as theemitting dopant whereas Comparative Device Example 6 uses E4 as theemitting dopant. Compound 35 and E4 are both tris homoleptic compounds(i.e., IrL₃) with a ligand which has a twisted aryl group attached to 5position of 2-phenylpyridine. Their only difference is that in Compound35, the aryl is a 2-methylphenyl group whereas in E4, the aryl is a2,6-dimethylphenyl.

The extra methyl group in E4 makes the twisted aryl twist more than thatin Compound 35. The result (Table 8) shows that the device with Compound35 (Device Example 28, RT_(80%)=200 h) is much more stable than thedevice with E4 (Comparative Device Example 6, RT_(80%)=42 h). It isbelieved that a more conjugated ligand can lead to more stable emittingdopant. The conjugation in the series of E3, Compound 35 and E4decreases as the number of methyl group increases from zero to one totwo (i.e., increasing twist between pyridine and the C-ring). It istherefore reasonable to believe a device with E3 as the emitting dopantwould be even more stable than a device with Compound 35 as the emittingdopant. However, the increase in conjugation also causes red shift inthe emission of the corresponding Ir complexes. Table 7 shows that E3(Comparative Device Example 5) has a λ_(max) of 548 nm and CIE of(0.430, 0.560), whereas Compound 35 (Device Example 28) has a λ_(max) of532 nm and CIE of (0.368, 0.607) and E4 (Comparative Device Example 6)has a λ_(max) of 520 nm and CIE of (0.320, 0.632). Therefore, althoughE3 may be more stable, but the emission is yellow which is not suitablefor full color RGB display. Compound 35 has conjugation between E3 andE4, achieving much improved stability over E4 (little conjugation) andbetter green color over E3 (too much conjugation).

Compounds are provided, comprising a ligand L having an alkylsubstituent and an aryl substituent such that the substituent aryl istwisted and having the structure:

B and C are each independently a 5 or 6-membered carbocyclic orheterocyclic ring. A-B represents a bonded pair of carbocyclic orheterocyclic rings coordinated to a metal M via a nitrogen atom in ringA and an sp² hybridized carbon atom in ring B. A-C represents a bondedpair of carbocyclic and heterocyclic rings. R_(a), R_(b), and R_(c) mayrepresent mono, di, tri, or tetra substitutions. R_(a), R_(b), and R_(c)are independently selected from the group consisting of hydrogen, alkyl,alkoxy, amino, alkenyl, alkynyl, arylkyl, aryl, and heteroaryl. X₁, X₂,X₃, X₄, X₅, X₆, X₇, X₈, and X₉ are independently selected from carbonand nitrogen. Preferably, A is pyridine. R₁ and R₂ are independentlyselected from the group consisting of hydrogen, alkyl, alkoxy, amino,alkenyl, alkynyl, arylkyl, aryl, and heteroaryl. At least one of R₁, R₂,and the R_(a) substituents adjacent to C is not hydrogen. Preferably,only one of R₁, R₂, and the R_(a) substituents adjacent to C is nothydrogen. Preferably, only one of R₁, R₂, and the R_(a) substituentsadjacent to C is alkyl. More preferably, only one of R₁, R₂, and theR_(a) substituents adjacent to C is ethyl. Most preferably, only one ofR₁, R₂, and the R_(a) substituents adjacent to C is methyl. The ligand Lis coordinated to the metal M having an atomic number greater than 40.Preferably, the metal M is Ir.

Particular compounds are provided having the structure:

m is the oxidation state of the metal M. n is at least 1. L′ is amonoanionic bidentate ligand. Preferably, only one of R₁, R₂, and theR_(a) substituents adjacent to C is not hydrogen. Preferably, only oneof R₁, R₂, and the R_(a) substituents adjacent to C is alkyl. Morepreferably, only one of R₁, R₂, and the R_(a) substituents adjacent to Cis ethyl. Most preferably, only one of R₁, R₂, and the R_(a)substituents adjacent to C is methyl. Preferably, A is pyridine.

Particular examples of compounds having Formula II are provided. Thecompound is selected from the group consisting of:

R is not hydrogen. Preferably, R is alkyl.

Specific examples of compounds having Formula II are provided. In oneaspect, the compound is selected from the group consisting of:

Preferably, the compound is selected from the group consisting ofCompound 21, Compound 22, Compound 25, Compound 29, Compound 30,Compound 31 and Compound 34.

In one aspect, compounds are provided wherein the compound is selectedfrom the group consisting of:

At least one of R₁, R₂, R₃, and R₄ are not hydrogen. R₅ is selected fromthe group consisting of hydrogen, alkyl, alkoxy, amino, alkenyl,alkynyl, arylkyl, aryl, and heteroaryl.

As discussed above, the position of the twist inducing substituentadjacent to the substituent aryl ring (i.e., C ring) results in thetwisting of the C ring out of plane thereby reducing packing andoffering a wide range of tunability in terms of evaporation temperature,solubility, energy levels, device efficiency and narrowness of theemission spectrum. In addition, the substituents can be stablefunctional groups chemically as well as in device operation.

In one aspect, R₁ and R₂ are hydrogen and one of R₃ and R₄ is alkyl.Exemplary compounds may include Compounds 21-24 and 29-34, 36 and 37. Inanother aspect, one of R₁ and R₂ is alkyl and R₃ and R₄ are hydrogen.Exemplary compounds may include Compounds 25-28 and 35.

In another aspect, the compound is selected from the group consistingof:

The compounds having Formula II include homoleptic compounds andheteroleptic compounds. Non-limiting examples of homoleptic compoundinclude Compounds 21-24 and 35. Non-limiting examples of heterolepticcompounds include Compounds 25-34, 36 and 37.

Particular heteroleptic compounds are provided where the compound has aligand L′ selected from the group consisting of:

R′₁, R′₂ and R′₃ are independently selected from the group consisting ofhydrogen, alkyl, alkoxy, amino, alkenyl, alkynyl, arylkyl, aryl, andheteroaryl.

Twisted aryl containing compounds having an alkyl substituent present onthe pyridine ring of the 2-phenylpyridine ligand also having the arylsubstituent may be preferred. In particular, preferred compounds areprovided wherein the compound selected from the group consisting ofCompound 21-Compound 23, Compound 29-Compound 31, Compound 34, Compound36 and Compound 37. Even more preferred compounds are Compound 21,Compound 22, Compound 29-31, Compound 34, Compound 36 and Compound 37which has the alkyl group at the 4-position of the 2-phenylpyridineligand (i.e., para to the pyridine nitrogen). It is because suchsubstitution can provide the twist and also a slight blue shiftingeffect to make the compound emit in a deeper green emission. Forexample, Device Example 13 has λ_(max) of 525 nm and CIE of (0.342,0.612) whereas Device Example 19 has λ_(max) of 532 nm and CIE of(0.372, 0.599). Example 13 uses Compound 12 as the emitting dopant whichhas a methyl group at the 4-position of the 2-phenylpyridine ligandwhereas Example 19 uses Compound 25 as the emitting dopant which has amethyl group at the 2-position of the twist phenyl. Although the twistinduced structurally in both cases is believed to be similar, the methylpara to the pyridine nitrogen provides electron donating effect, raisingthe LUMO energy level of complex and also the triplet energy, resultingin a blue shift in emission.

An organic light emitting device is also provided. The device has ananode, a cathode, and an organic layer disposed between the anode andthe cathode, where the organic layer comprises a compound having FormulaI, as described above. Selections for the substituents described aspreferred for the compounds having Formula I are also preferred for usein a device that comprises a compound having Formula I. These selectionsinclude those described for the metal M; the formulas II-VI; R, R₁, R₂,and R_(a) substituents adjacent to C; the position of ring C; and ringsA, B, and C.

In one aspect, the device comprises a compound having Formula II, asdescribed above. Preferably, the metal M is Ir. Preferably, A ispyridine. In another aspect, the device comprises a compound havingFormula III or Formula IV, as described above. Devices containing acompound wherein only one of R₁, R₂, and the R_(a) substituents adjacentto C is alkyl may also be preferred. In another aspect, the devicecomprises a compound having Formula V or Formula VI, as described above.Certain devices are provided wherein the device contains a compoundselected from the group consisting of Compound 21-Compound 37.Preferably, the device contains Compound 21, Compound 22, Compound 25,Compound 29, Compound 30, Compound 31 or Compound 34.

In one aspect, devices are provided wherein the organic layer is anemissive layer and the compound having the formula of Formula I is anemitting dopant. Moreover, the organic layer may further comprise ahost. Preferably, the host has the formula:

R′₁, R′₂, R′₃, R′₄, R′₅, and R′₆ are independently selected from thegroup consisting of hydrogen, alkyl, alkoxy, amino, alkenyl, alkynyl,arylkyl, aryl, and heteroaryl.

A consumer product comprising a device is also provided. The devicecomprises an anode, a cathode, and an organic layer disposed between theanode and the cathode, where the organic layer comprises a compoundhaving Formula I, as described above. Selections for the substituentsdescribed as preferred for the compounds having Formula I are alsopreferred for use in a consumer product containing a device thatcomprises a compound having Formula I. These selections include thosedescribed for the metal M; the formulas II-VI; R, R₁, R₂, and R_(A)substituents adjacent to C; the position of ring C; and rings A, B, andC.

Additionally, novel methods are provided for making homoleptic Ir (III)compounds (illustrated in FIG. 9). A commonly used method of makinghomoleptic Ir (III) compounds involves heating a mixture of Ir(acac)₃with the ligand at reluxing glycerol (˜180° C.) or without solventat >230° C. Such high temperature of reaction can cause problems such asthermal degradation of the ligand and the resulting complex. Therefore,it is highly desirable to provide a new method for making homoleptic Ir(III) compounds at lower temperatures. The methods, as described herein,can be used to make homoleptic Ir (III) compounds that may beadvantageously used in OLEDs. In particular, a first method for making ahomoleptic Ir (III) compound having is provided. The first method may beused to synthesize compounds having an alkyl group which is not adjacentto the nitrogen in the heteroleptic ring of the ligand. Compounds 21,22, and 24, for example, may be synthesized using the first methodprovided. A second method for making homoleptic Ir (III) compounds isalso provided. The second method may be used to make compounds having analkyl group which is adjacent to the nitrogen in the heterocyclic ringof the ligand. Compound 23, for example, may be synthesized using thesecond method provided.

A first method for making a homoleptic Ir(III) complex is provided. Thefirst method comprising:

reacting

with

in the presence of a low boiling alcohol to form

At least one of R_(A) and R_(B) is an alkyl group and the alkyl group isnot adjacent to the nitrogen on the pyridine ring. S is a neutralligand. X is a counterion. Preferably, X is triflate. A and B are eachindependently a 5 or 6-membered carbocyclic or heterocyclic ring. A-Brepresents a bonded pair of carbocyclic or heterocyclic ringscoordinated to the iridium via a nitrogen atom on ring A and an sp²hybridized carbon atom on ring B. Each of R_(A) and R_(B) may representmono, di, tri, or tetra substitutions. R_(A) and R_(B) are eachindependently selected from the group consisting of hydrogen, alkyl,alkoxy, amino, alkenyl, alkynyl, arylkyl, aryl, and heteroaryl.

Low boiling alcohols may include any alcohol which has a boilingtemperature equal to or less than 108° C. In one aspect, the low boilingalcohol is selected from the group consisting of methanol, ethanol,n-propanol, isopropanol, n-butanol, a 1:1 ratio of ethanol and methanol,2-methoxyethanol, and 2-ethoxyethanol. Preferably, the low boilingalcohol is selected from the group consisting of isopropanol which boilsat 108° C., ethanol which boils at 78° C., and a 1:1 ratio of ethanoland methanol which boils between 64° C. and 78° C. More preferably, thelow boiling alcohol is ethanol or a 1:1 ratio of ethanol and methanol.Most preferably, the low boiling alcohol is a 1:1 ratio of ethanol andmethanol.

Preferably, A is:

C is a 5 or 6-membered carbocyclic or heterocyclic ring. A-C representsa bonded pair of carbocyclic or heterocyclic rings. R_(A) and R_(C) mayrepresent mono, di, tri, or tetra substitutions. R_(A) and R_(C) areindependently selected from the group consisting of hydrogen, alkyl,alkoxy, amino, alkenyl, alkynyl, arylkyl, aryl, and heteroaryl. X₁, X₂,X₃, X₄, X₅, X₆, X₇, X₈, and X₉ are independently selected from carbonand nitrogen. R₁ and R₂ are independently selected from the groupconsisting of hydrogen, alkyl, alkoxy, amino, alkenyl, alkynyl, arylkyl,aryl, and heteroaryl. At least one of R₁, R₂, and the R_(a) substituentsadjacent to C is not hydrogen.

In one aspect, the first method comprises

reacting

with

in the presence of a low boiling alcohol to form

Specific compounds, including Compounds 21, 22, and 24, may be formedusing this method.

A second method for making homoleptic Ir (III) compounds is provided.The second method comprises:

reacting

with

in the absence of solvent to form

At least one of R_(A) and R_(B) is an alkyl group and the alkyl group isadjacent to the nitrogen on the pyridine ring. S is a neutral ligand. Xis a counterion. Preferably, X is triflate. A and B are eachindependently a 5 or 6-membered carbocyclic or heterocyclic ring. A-Brepresents a bonded pair of carbocyclic or heterocyclic ringscoordinated to the iridium via a nitrogen atom on ring A and an sp²hybridized carbon atom on ring B. Each of R_(A) and R_(B) may representmono, di, tri, or tetra substitutions. R_(A) and R_(B) are eachindependently selected from the group consisting of hydrogen, alkyl,alkoxy, amino, alkenyl, alkynyl, arylkyl, aryl, and heteroaryl.

Preferably, A is:

C is a 5 or 6-membered carbocyclic or heterocyclic ring. A-C representsa bonded pair of carbocyclic or heterocyclic rings. R_(A) and R_(C) mayrepresent mono, di, tri, or tetra substitutions. R_(A) and R_(C) areindependently selected from the group consisting of hydrogen, alkyl,alkoxy, amino, alkenyl, alkynyl, arylkyl, aryl, and heteroaryl. X₁, X₂,X₃, X₄, X₅, X₆, X₇, X₈, and X₉ are independently selected from carbonand nitrogen. R₁ and R₂ are independently selected from the groupconsisting of hydrogen, alkyl, alkoxy, amino, alkenyl, alkynyl, arylkyl,aryl, and heteroaryl. At least one of R₁, R₂, and the R_(a) substituentsadjacent to C is not hydrogen.

In one aspect, the second method comprises:

reacting

with

in the absence of solvent to form

Specific compounds, including Compound 23, may be formed using thismethod. In particular, Compound 23 can be made using the syntheticmethod, as follows:

reacting

with

in the absence solvent for 16 h at 130° C. to form

The materials described herein as useful for a particular layer in anorganic light emitting device may be used in combination with a widevariety of other materials present in the device. For example, emissivedopants disclosed herein may be used in conjunction with a wide varietyof hosts, transport layers, blocking layers, injection layers,electrodes and other layers that may be present. The materials describedor referred to below are non-limiting examples of materials that may beuseful in combination with the compounds disclosed herein, and one ofskill in the art can readily consult the literature to identify othermaterials that may be useful in combination.

In addition to and/or in combination with the materials disclosedherein, many hole injection materials, hole transporting materials, hostmaterials, dopant materials, exiton/hole blocking layer materials,electron transporting and electron injecting materials may be used in anOLED. Non-limiting examples of the materials that may be used in an OLEDin combination with materials disclosed herein are listed in Table 1below. Table 1 lists non-limiting classes of materials, non-limitingexamples of compounds for each class, and references that disclose thematerials.

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EXPERIMENTAL Compound Examples

Some heteroleptic Ir (III) complexes were synthesized as follows:

Example 1 Synthesis of Compound 1

Synthesis of 2-phenyl-4-bromopyridine

A mixture was prepared of 2,4-dibromopyridine (10 g, 42.21 mmol),phenylboronic acid (5.1 g, 42.21 mmol), and potassium carbonate (11.7 g,84.42 mmol) in 100 mL dimethoxyethane and 40 mL of water. Nitrogen wasbubbled directly into the mixture for 30 minutes. Next,tetrakis(triphenylphosphine)palladium(0) was added (244 mg, 2.11 mmol)and the mixture was heated to reflux under nitrogen overnight. Themixture was cooled and diluted with ethyl acetate and water. The layerswere separated and the aqueous layer was extracted with ethyl acetate.The organic layers were washed with brine, dried over magnesium sulfate,filtered, and evaporated to a residue. The residue was purified bycolumn chromatography eluting with 0, 2, and 5% ethyl acetate/hexanes.Obtained 4.28 g of a yellow liquid (43%).

Synthesis of2-phenyl-4(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2yl)pyridine

A mixture was prepared of 2-phenyl-4-bromopyridine (4.28 g, 18.28 mmol),bis(pinacolato)diboron (9.29 g, 36.57 mmol), and potassium acetate (5.38g, 54.84 mmol) in 100 mL of dioxane. Nitrogen was bubbled directly intothe mixture for 30 minutes.Dichloro[1,1′-ferrocenylbis(diphenylphosphine)]palladium(II)dichloromethane (448 mg, 0.55 mmol) was added, and nitrogen bubbled foranother 15 minutes. The reaction mixture was heated to 90° C.internally. After 1 h the reaction was complete, and the heat was shutoff. The solvent was evaporated to an oil. The oil was purified byKugelrohr at 200° C. to remove excess bis(pinacolato)diboron. Theresidue left in the boiling pot was dissolved in ethyl acetate andfiltered through magnesium sulfate, rinsed with ethyl acetate, and thefiltrate was evaporated. Used as described in the next step. Yield wasapproximately 4 g of product.

Synthesis of PPY Dimer

14.7 g (0.04 mol) of iridium chloride and 26.0 g (0.17 mol) of2-phenylpyridine was placed in a 1 L round bottomed flask. 300 ml of2-ethocyethanol and 100 ml of water was added. The mixture was refluxedunder nitrogen atmosphere overnight. After having cooled to roomtemperature, the precipitate was filtered and washed with methanol.After drying, 22 g of dimer was obtained. (99% yield).

Synthesis of Triflate

22 g of dimer was dissolved in 1 L of dichloromethane. 10.5 g (0.04 mol)of silver triflate was added to the solution. 25 ml of methanol was thenadded. The solution was stirred for 5 h. The silver chloride wasfiltered off. The solvent was evaporated. 26 g of product was obtained.The solid was used for next step without further purification.

Synthesis of Boronic Ester Precursor

A mixture was prepared of the triflate (4.6 g, 7.11 mmol) and2-phenyl-4(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2yl)pyridine (˜4 g,˜14.23 mmol) in 100 mL of ethanol. The mixture was heated at reflux for6 h under nitrogen. The solvent was evaporated and hexanes was added. Asold was filtered off which was washed with hexanes. The solid waspurified by column chromatography eluting with dichloromethane and latersome methanol was added. Obtained 0.92 g of an orange solid(approximately 17%).

Synthesis of Compound 1

Mixed the boronic ester precursor (0.92 g, 1.18 mmol), bromobenzene (0.6g, 3.54 mmol), 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (19 mg,0.047 mmol), and potassium phosphate tribasic (0.82 g, 3.54 mmol) in 50mL of toluene and 5 mL of water. Bubbled nitrogen directly into themixture for 30 minutes after whichtris(dibenzylideneacetone)dipalladium(0) (11 mg, 0.0118 mmol) was added.Nitrogen was bubbled for another 5 minutes then the reaction mixture washeated to reflux for 1 h under nitrogen. The mixture was cooled and anorange solid precipitated out. The solid was filtered off and washedwith hexanes followed by methanol. Some solid was seen in filtrate sothe filtrate was evaporated and methanol was added. More orange solidwas filtered off. All the solid was purified by column chromatographyeluting with 50% dichloromethane/hexanes. The solid was sublimed at 280°C. Obtained 0.53 g (62%).

Example 2 Synthesis of Compound 2

The following synthesis could be used to make Compound 2.

Synthesis of 2-phenyl-5-bromopyridine

A mixture is prepared of 2,5-dibromopyridine (10 g, 42.21 mmol),phenylboronic acid (5.1 g, 42.21 mmol), and potassium carbonate (11.7 g,84.42 mmol) in 100 mL dimethoxyethane and 40 mL of water. Nitrogen isbubbled directly into the mixture for 30 minutes. Next,tetrakis(triphenylphosphine)palladium(0) was added (244 mg, 2.11 mmol)and the mixture is heated to reflux under nitrogen overnight. Themixture is cooled and diluted with ethyl acetate and water. The layersare separated and the aqueous layer is extracted with ethyl acetate. Theorganic layers are washed with brine, dried over magnesium sulfate,filtered, and evaporated to a residue. The residue is purified by columnchromatography eluting with 0, 2, and 5% ethyl acetate/hexanes.

Synthesis of2-phenyl-5-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)pyridine

A mixture is prepared of 2-phenyl-4-bromopyridine (4.28 g, 18.28 mmol),bis(pinacolato)diboron (9.29 g, 36.57 mmol), and potassium acetate (5.38g, 54.84 mmol) in 100 mL of dioxane. Nitrogen is bubbled directly intothe mixture for 30 minutes.Dichloro[1,1′-ferrocenylbis(diphenylphosphine)]palladium(II)dichloromethane (448 mg, 0.55 mmol) is added. The reaction mixture isheated to 90° C. internally for 3 h. The solvent is evaporated to anoil. The oil was purified by Kugelrohr to remove excessbis(pinacolato)diboron. The residue left in the boiling pot is dissolvedin ethyl acetate and filtered through magnesium sulfate, rinsed withethyl acetate, and the filtrate is evaporated. The product can be usedwithout purification in the next step.

Synthesis of Boronic Ester Precursor

A mixture is prepared of the triflate (4.6 g, 7.11 mmol) and2-phenyl-5-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2yl)pyridine (˜4 g,˜14.23 mmol) in 100 mL of ethanol. The mixture is heated at reflux for24 h under nitrogen. The solvent is evaporated and hexanes is added. Asold is filtered off which is washed with hexanes. The solid is purifiedby column chromatography eluting with dichloromethane and later somemethanol is added.

Synthesis of Compound 2

The boronic ester precursor (0.92 g, 1.18 mmol), bromobenzene (0.6 g,3.54 mmol), 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (19 mg,0.047 mmol), and potassium phosphate tribasic (0.82 g, 3.54 mmol) aremixed in 50 mL of toluene and 5 mL of water. Nitrogen is bubbleddirectly into the mixture for 30 minutes after whichtris(dibenzylideneacetone)dipalladium(0) (11 mg, 0.0118 mmol) is added.Nitrogen is bubbled for another 5 minutes then the reaction mixture isheated to reflux for 1 h under nitrogen. The mixture is cooled and anorange solid formed. The solid is filtered off and washed with hexanesfollowed by methanol. The solid is purified by column chromatographyeluting with 50% dichloromethane/hexanes.

Example 3 Synthesis of Compound 3

Irppy intermediate (0.70 g, 0.90 mmol), 2-bromopyrimidine (0.71 g, 4.5mmol), tris(dibenzylideneacetone)dipalladium(0) [Pd₂(dba)₃] (0.01 g, 1mol %), tricyclohexylphosphine (0.05 g, 0.18 mmol) and potassiumphosphate tribasic (K₃PO₄) (0.7 g, 3.3 mmol) were weighed into a 100 mL3-neck round bottom flask. 40 mL toluene and 10 mL water were added tothe reaction vessel. The reaction mixture was degassed by bubblingnitrogen directly in the mixture for an hour. The solution was heated toreflux for 2 h. After cooling, the product was filtered, dissolved inmethylene chloride and chromatographed using silica gel with methylenechloride:hexanes (50:50) as the mobile phase. The solvent was removedusing the rotary evaporator and the product dried under vacuum to give0.6 g of product (90% yield).

Example 4 Synthesis of Compound 4

Irppy intermediate (1.0 g, 1.3 mmol), 2-bromopyridine (1.01 g, 6.4mmol), tris(dibenzylideneacetone)dipalladium(0) [Pd₂(dba)₃] (0.05 g, 1mol %), tricyclohexylphosphine (0.08 g, 5 mol %) and potassium phosphatetribasic (K₃PO₄) (4.0 g, 19.0 mmol) were weighed into a 100 mL 3-neckround bottom flask. 50 mL dioxane and 10 mL water were added to thereaction vessel. The reaction mixture was degassed by bubbling nitrogendirectly in the mixture for an hour. The solution was heated to refluxfor 2 h. After cooling, the product was filtered, dissolved in methylenechloride and chromatographed using silica gel with methylenechloride:hexanes (50:50) as the mobile phase. The solvent was removedusing the rotary evaporator and the product dried under vacuum to give0.8 g of product (86% yield).

Example 5 Synthesis of Compound 5

Irppy intermediate (1.50 g, 1.90 mmol), 3-bromothiophene (1.61 g, 9.6mmol), tris(dibenzylideneacetone)dipalladium(0) [Pd₂(dba)₃] (0.02 g, 1mol %), tricyclohexylphosphine (0.04 g, 4 mol %) and potassium phosphatetribasic (K₃PO₄) (1.2 g, 5.6 mmol) were weighed into a 250 mL 3-neckround bottom flask. 100 mL toluene and 10 mL water were added to thereaction vessel. The reaction mixture was degassed by bubbling nitrogendirectly in the mixture for an hour. The solution was heated to refluxfor 2 h. After cooling, the product was filtered, dissolved in methylenechloride and chromatographed using silica gel with methylenechloride:hexanes (50:50) as the mobile phase. The solvent was removedusing the rotary evaporator and the product dried under vacuum to give1.0 g of product (74% yield).

Example 6 Synthesis of Compound 6

Irppy intermediate (1.50 g, 1.90 mmol), 3-bromothianaphthene (2.0 g, 9.6mmol), tris(dibenzylideneacetone)dipalladium(0) [Pd₂(dba)₃] (0.08 g, 1mol %), tricyclohexylphosphine (0.2 g, 0.5 mmol) and potassium phosphatetribasic (K₃PO₄) (1.2 g, 5.6 mmol) were weighed into a 250 mL 3-neckround bottom flask. 100 mL toluene and 10 mL water were added to thereaction vessel. The reaction mixture was degassed by bubbling nitrogendirectly in the mixture for an hour. The solution was heated to refluxfor 2 h. After cooling, the product was filtered, dissolved in methylenechloride and chromatographed using silica gel with methylenechloride:hexanes (50:50) as the mobile phase. The solvent was removedusing the rotary evaporator and the product dried under vacuum to give1.2 g of product (80% yield).

Example 7 Synthesis of Compound 7

Synthesis of 2-(3-bromophenyl)pyridine

2-bromopyridine (75.0 g, 475 mmol), 3-bromophenylboronic acid (104.8 g,520 mmol), palladium acetate (2.6 g, 2.5 mol %), triphenylphosphine(5.37 g, 5 mol %) and potassium carbonate (196.0 g, 1425 mmol) wasplaced in a 2 L 3-neck round bottom flask. 500 mL of dimethoxyethane and500 mL of H₂O was added to the flask. Nitrogen was bubbled through thesolution for 30 minutes and then the solution was refluxed for 8 h in anatmosphere of nitrogen. The reaction was then allowed to cool to roomtemperature and the organic phase was separated from the aqueous phase.The aqueous phase was washed with ethylacetate and the organic fractionswere combined and dried over magnesium sulfate and the solvent removedunder vacuum. The product was chromatographed using silica gel withethylacetate and hexanes as the eluent. The solvent was removed to give84.0 g of a clear oil (76% yield).

Synthesis of2-(3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)pyridine

2-(3-bromophenyl)pyridine (25.0 g, 107 mmol), bis(pinacolato)diboron(54.2 g, 214 mmol), Pd(dppf)₂Cl₂ (1.0 g, 10 mol %), and potassiumacetate (31.5 g, 321 mmol) were placed in 1 L round bottom flask. 600 mLof dioxane was then added to the flask. Nitrogen was bubbled into thereaction mixture for 1 h and then the flask was heated to 90° C. for 12h in an atmosphere of nitrogen. The dioxane was removed under reducedpressure by a rotary evaporator. The dark solid was dissolved in 400 mLof dichloromethane and passed through a 2 inch thick silica gel plug.The dichloromethane was removed under reduced pressure by a rotaryevaporator to leave a yellow oil. The product was then distilled using aKuglerohr apparatus to give 23 g of a white solid (77% yield).

Synthesis of Irppy Intermediate

Irppy triflate (17.5 g, 25 mmol) and 3 molar equivalent2-(3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)pyridine (21.50g, 117 mmol) was placed in a 2 L 3 neck round bottomed flask. 600 mL ofalcohol was added to the reaction mixture. The reaction mixture wasdegassed by bubbling nitrogen directly in the mixture for an hour. Thereaction mixture was then refluxed (internal temp of the reactionmixture was 78 degrees) for overnight. After about 18 h the product hadalready precipitated from the hot reaction mixture. After cooling toroom temperature 200 mL isopropanol was added to precipitate any moreproduct from the reaction mixture. The reaction mixture was thenfiltered and the product/residue was washed with isopropanol (to removeexcess ligand) and then air dried to give 12 g of product (60% yield).

Synthesis of Compound 7

Irppy intermediate (0.50 g, 0.64 mmol), bromobenzene (0.5 g, 3.2 mmol),tris(dibenzylideneacetone)dipalladium(0) [Pd₂(dba)₃] (0.006 g, 0.0064mmol), 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (0.10 g, 0.025mmol) and potassium phosphate tribasic (K₃PO₄) (0.4 g, 1.92 mmol) wereweighed into a 100 mL 3 neck round bottom flask. 40 mL toluene and 10 mLwater were added to the reaction vessel. The reaction mixture wasdegassed by bubbling nitrogen directly in the mixture for an hour. Thesolution was heated to reflux for 2 h. After cooling, the product wasfiltered, dissolved in methylene chloride and chromatographed usingsilica gel with methylene chloride:hexanes (50:50) as the mobile phase.The solvent was removed using the rotary evaporator and the productdried under vacuum to give 0.5 g of product (95% yield).

Example 8 Synthesis of Compound 2

This following alternate synthesis was used to make Compound 2.

Synthesis of 2,5-diphenylpyridine

2,5-dibromopyridine (10 g, 42 mmol), phenylboronic acid (13.4 g, 110mmol), dicyclohexyl(2′,6′-dimethoxybiphenyl-2-yl)phosphine (S-Phos) (0.7g, 1.6 mmol), and potassium phosphate (22 g, 105 mmol) were mixed in 200mL of toluene and 20 mL of water. Nitrogen is bubbled directly into themixture for 30 minutes. Next, Pd₂(dba)₃ was added (0.38 g, 0.4 mmol) andthe mixture was heated to reflux under nitrogen for 2 h. The mixture wascooled and the organic layer was separated. The organic layers arewashed with brine, dried over magnesium sulfate, filtered, andevaporated to a residue. The residue was purified by columnchromatography eluting with 10% ethyl acetate/hexanes. 7 g of desiredproduct was obtained after purification. (91.8% yield)

Synthesis of Compound 2

The iridium triflate precursor (2.5 g, 3.5 mmol) and2,5-diphenylpyridine (2.4 g, 11 mmol) were mixed in 200 mL of ethanol.The mixture was heated at reflux for 24 h under nitrogen. Precipitateformed during reflux. The reaction mixture was filtered through a celitebed. The product was washed with methanol and hexanes. The solid wasdissolved in dichloromethane and purified by column using 1:1 ofdichloromethane and hexanes. 1.2 g of pure product was obtained afterthe column purification. (HPLC purity: 99.8%)

Example 9 Alternate Synthesis of Compound 7

The following alternate synthesis was used to make Compound 2.

The iridium triflate precursor (2.5 g, 3.5 mmol) and2-(biphenyl-3-yl)pyridine (2.4 g, 11 mmol) were mixed in 200 mL ofethanol. The mixture was heated at reflux for 24 h under nitrogen.Precipitate formed during reflux. The reaction mixture was filteredthrough a celite bed. The product was washed with methanol and hexanes.The solid was dissolved in dichloromethane and purified by column using1:1 of dichloromethane and hexanes. 1.5 g of pure product was obtainedafter the column purification. (HPLC purity: 99.6%)

Example 10 Synthesis of Compound 8

The iridium triflate precursor (2.5 g, 3.5 mmol) and2-(biphenyl-4-yl)pyridine (2.4 g, 11 mmol) were mixed in 100 mL ofethanol. The mixture was heated at reflux for 24 h under nitrogen.Precipitate formed during reflux. The reaction mixture was filteredthrough a celite bed. The product was washed with methanol and hexanes.The solid was dissolved in dichloromethane and purified by column using1:1 of dichloromethane and hexanes. 1.2 g of pure product was obtainedafter the column purification. (HPLC purity: 99.8%)

Example 11 Synthesis of Compound 9

The iridium triflate precursor (2.5 g, 3.5 mmol) and2-(biphenyl-4-yl)-4-methylpyridine (2.6 g, 11 mmol) were mixed in 100 mLof ethanol. The mixture was heated at reflux for 24 h under nitrogen.Precipitate formed during reflux. The reaction mixture was filteredthrough a celite bed. The product was washed with methanol and hexanes.The solid was dissolved in dichloromethane and purified by column using1:1 of dichloromethane and hexanes. 1.3 g of pure product was obtainedafter the column purification. (HPLC purity: 99.9%)

Example 12 Synthesis of Compound 10

The iridium triflate precursor (2.0 g, 2.7 mmol) and2-(biphenyl-4-yl)-4-methylpyridine (2.0 g, 8.2 mmol) were mixed in 60 mLof ethanol. The mixture was heated at reflux for 24 h under nitrogen.Precipitate formed during reflux. The reaction mixture was filteredthrough a celite bed. The product was washed with methanol and hexanes.The solid was dissolved in dichloromethane and purified by column using1:1 of dichloromethane and hexanes. 1.6 g of pure product was obtainedafter the column purification. (HPLC purity: 99.4%)

Example 13 Synthesis of Compound 11

The iridium triflate precursor (1.2 g, 1.6 mmol) and2,5-diphenylpyridine (1.2 g, 4.8 mmol) were mixed in 50 mL of ethanol.The mixture was heated at reflux for 24 h under nitrogen. Precipitateformed during reflux. The reaction mixture was filtered through a celitebed. The product was washed with methanol and hexanes. The solid wasdissolved in dichloromethane and purified by column using 1:1 ofdichloromethane and hexanes. 1.0 g of pure product was obtained afterthe column purification. (HPLC purity: 99.3%)

The reaction of the iridium triflate intermediate with the second ligandin an organic solvent, as shown for Compound 11, often produces amixture because of the ligand scrambling during the reaction.Interestingly, during the synthesis of Compound 11, no significantscrambling occurred.

However, the synthesis of Compound 7 using this method resulted insignificant scrambling despite the structural similarity betweenCompounds 11 and 7 (i.e., Compound 7 is identical to Compound 7 exceptfor a methyl group on the phenyl pyridine ligand). In particular, theiridium triflate intermediate was reacted with 2,5-diphenylpyridine inethanol under reflux condition. The product was a mixture of Compound 7and other two scrambled products as shown below. Due to the similarityof polarity of the compounds, it is very difficult to separate theseimpurities from Compound 7 using normal phase silica gel chromatography.

Example 14 Synthesis of Compound 12

The iridium triflate precursor (2.5 g, 3.5 mmol) and4-methyl-2,5-diphenylpyridine (2.6 g, 10.5 mmol) were mixed in 100 mL ofethanol. The mixture was heated at reflux for 24 h under nitrogen.Precipitate formed during reflux. The reaction mixture was filteredthrough a celite bed. The product was washed with methanol and hexanes.The solid was dissolved in dichloromethane and purified by column using1:1 of dichloromethane and hexanes. 1.2 g of pure product was obtainedafter the column purification. (HPLC purity: 99.9%)

Example 15 Synthesis of Compound 13

The iridium triflate precursor (2.5 g, 2.7 mmol) and2-(biphenyl-4-yl)-6-methylpyridine (2.0 g, 8.1 mmol) were put into a 20mL reaction tube. The reaction tube was evacuated and then refilled withnitrogen. The process was repeated three times. The mixture was heatedat 130° C. for 24 h under nitrogen. The reaction mixture was dissolvedin dichloromethane and purified by column using 1:1 of dichloromethaneand hexanes. 0.98 g of pure product was obtained after the columnpurification. (HPLC purity: 99.8%)

Example 16 Synthesis of Compound 14

The iridium triflate precursor (0.86 g, 1.15 mmol) and4-methyl-2,5-diphenylpyridine (0.85 g, 3.46 mmol) were mixed in 30 mL ofethanol. The mixture was heated at reflux for 24 h under nitrogen.Precipitate formed during reflux. The reaction mixture was filteredthrough a celite bed. The product was washed with methanol and hexanes.The solid was dissolved in dichloromethane and purified by column using1:1 of dichloromethane and hexanes. 0.7 g of pure product was obtainedafter the column purification. (HPLC purity: 99.5%)

The reaction of the iridium triflate intermediate with the second ligandin an organic solvent, as shown for Compound 11, often produces amixture of products because of ligand scrambling during the reaction.Interestingly, during the synthesis of Compounds 10, 11, and 14, nosignificant scrambling occurred. The content of the desired product inthe precipitate was higher than 99% in all cases.

In particular, the synthesis of Compound 7 using this method resulted insignificant scrambling despite the structural similarity betweenCompounds 11 and 7 (i.e., Compound 7 is identical to Compound 7 exceptfor a methyl group on the phenyl pyridine ligand). In particular, theiridium triflate intermediate was reacted with 2,5-diphenylpyridine inethanol under reflux condition. The product was a mixture of Compound 7and other two scrambled products as shown below. Due to the similarityof polarity of the compounds, it is very difficult to separate theseimpurities from Compound 7 using normal phase silica gel chromatography.

Example 17 Synthesis of Compound 21

Synthesis of 2,5-diphenyl-4-methylpyridine

Phenylboronic acid (72.9 g, 598 mmol), 2,5-dibromo-4-methylpyridine (50g, 199 mmol), 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (3.3 g, 8mmol), potassium phosphate tribasic monohydrate (137 g, 595 mmol), 650mL of toluene and 150 mL of water were placed in a 2 L round-bottomflask. Nitrogen was bubbled directly into the reaction mixture for 30min after which tris(dibenzylideneacetone)dipalladium(0) (1.79 g, 1.96mmol) was added. Nitrogen was bubbled into the reaction mixture foranother 15 min before the reaction mixture was heated to reflux for 16 hunder nitrogen. After the reaction was completed the mixture was cooledand the organic layer was separated from the aqueous layer. The organiclayer was washed with a saturated brine solution and then dried overmagnesium sulfate. The solution was filtered, and the solvent wasremoved under vacuum to give a yellow solid as the crude. The crude waspurified by column chromatography using silica gel as the stationaryphase and 10% ethyl acetate in hexanes as the mobile phase. The productwas further purified by recrystallization from hexanes. 42.6 g ofdesired product was obtained after purification (87.2% yield).

Synthesis of Ir Dimer

IrCl₃.3H₂O (7.54 g, 20.4 mol) and 2,5-diphenyl-4-methylpyridine (15.0 g,61 mol) were placed in a 1 L round bottomed flask. 100 mL of2-ethoxyethanol and 35 mL of water were then added. The mixture wasrefluxed under nitrogen atmosphere for 16 h. The reaction mixture wascooled to room temperature and the precipitate was filtered and washedwith methanol followed by hexanes. 13.6 g of the iridium dimer wasobtained (99% yield).

Synthesis of Ir Triflate

13.3 g of the iridium dimer was dissolved in 1.5 L of dichloromethane.Silver triflate (5.11 g, 19.9 mmol) was dissolved in 500 mL ofisopropanol and added to the iridium dimer solution. The resultingmixture was stirred for 18 h at room temperature. The solution was thenpoured through a celite plug to remove silver chloride and the solventwas evaporated under vacuum to give 17.0 g of the iridium triflate. Thesolid was used for the next step without further purification.

Synthesis of Compound 21

The iridium triflate (17.0 g, 17.9 mmol) and a 3 molar equivalent of2,5-diphenyl-4-methylpyridine (13.1 g, 53.7 mmol) were placed in a 1 Lround bottom flask. 150 mL of ethanol was added and the reaction mixturewas refluxed for 16 h. Celite was added to the cooled solution and themixture was poured onto a 2 inch bed of silica gel. The silica bed wasthen washed twice with ethanol (2×50 mL), followed by hexanes (2×50 mL).The product was then eluted through a silica gel plug withdichloromethane. Most of the dichloromethane was removed under vacuumand the product was precipitated with 2-propanol and filtered, washedwith hexanes and dried to give 9.69 g product (90.6% yield).

Example 18 Synthesis of Compound 22

Synthesis of 2-amino-4-ethyl-5-iodopyridine

4-ethyl-2-aminopyridine (10.0 g, 81.9 mmol) and potassium acetate (8.00g, 81.9 mmol) were dissolved in 100 mL of acetic acid and heated to 80°C. with continuous stirring. In a separate flask, iodomonochloride (13.2g, 81.9 mmol) was dissolved in 30 mL of acetic acid and added to theabove reaction mixture drop wise. Once the addition was completed, thereaction mixture was heated for an additional 4 h. Progress of thereaction was monitored by gas chromatography and HPLC. When the reactionwas completed, the reaction mixture was cooled to room temperature andquenched with an aqueous solution of saturated sodium bisulfite (10 mL).Acetic acid was removed under vacuum and the residue was dissolved inethyl acetate and neutralized with saturated NaHCO₃. The organic layerwas separated from the aqueous layer and the solvent was removed undervacuum. The crude was purified by silica gel column chromatographyeluting with 25% ethyl acetate/hexanes. 15 g of desired product wasobtained (74% yield).

Synthesis of 2-chloro-4-ethyl-5-iodopyridine

4-ethyl-5-iodopyridin-2-amine (15.0 g, 60.48 mmol) was dissolved in 140mL conc. HCl. NaNO₂ was dissolved in 40 mL of water and added drop wiseto the above solution at 0° C. Care was taken to prevent the temperatureof the reaction mixture from rising above 0° C. When all of the NaNO₂solution was added, the reaction mixture was allowed to warm up to roomtemperature and was stirred for a further 2 h at room temperature.Progress of the reaction was monitored by GC and HPLC. The reactionmixture was then re-cooled to 0° C. and the pH was adjusted to pH=12 bythe addition of sat. NaOH. The mixture was extracted withdichloromethane (2×200 mL) and the solvent removed under vacuum. Thecrude was purified by silica gel column chromatography eluting with 5%ethyl acetate/hexanes. 8.0 g of desired product was obtained afterpurification (49% yield).

Synthesis of 2,5-diphenyl-4-ethylpyridine

Phenylboronic acid (11.0 g, 90 mmol), 2-chloro-4-ethyl-5-iodopyridine(8.00 g, 30 mmol), 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (492mg, 1.2 mmol), and potassium phosphate tribasic (20.7 g, 90 mmol), 250mL, of toluene and 25 mL of water were placed in a 1 L round-bottomflask. Nitrogen was bubbled directly into the mixture for 30 min afterwhich tris(dibenzylideneacetone)dipalladium(0) (275 mg, 0.3 mmol) wasadded. Nitrogen was bubbled for another 15 min, then the reactionmixture was heated to reflux for 16 h under nitrogen. After the reactionwas completed the mixture was cooled and the organic layer was separatedfrom the aqueous layer. The organic layer was washed with saturatedbrine solution and dried over magnesium sulfate. The solution wasfiltered and the solvent was removed under vacuum to give a off-whitesolid. This crude was purified by silica gel column chromatographyeluting with 10% ethyl acetate/hexanes. 7.0 g of desired product wasobtained after purification (90.9% yield).

Synthesis of Ir Dimer

IrCl₃.3H₂O (1.5 g, 4.41 mmol) and 2,5-diphenyl-4-ethylpyridine (4.0 g,15.44 mmol) was placed in a 250 mL round bottomed flask. 30 mL of2-ethoxyethanol and 10 mL of water was added. The mixture was refluxedunder nitrogen atmosphere for 16 h. The reaction mixture was thenallowed to cool to room temperature and the precipitate was filtered andwashed with methanol followed by hexanes. After drying, 2.57 g of theiridium dimer was obtained (81% yield).

Synthesis of Ir Triflate

The iridium dimer (2.57 g, 1.725 mmol) was dissolved in 250 mL ofdichloromethane. Silver triflate (1.0 g, 3.8 mmol) was dissolved in 150mL of 2-propanol and added to the dimer solution. The resulting mixturewas stirred for 5 h. The solution was then poured through a celite plugto remove silver chloride. The solvent was evaporated under vacuum togive 3.2 g of the iridium triflate. The solid was used for next stepwithout further purification.

Synthesis of Compound 22

The iridium triflate (3.2 g) and 2,5-diphenyl-4-ethylpyridine (3.2 g)were placed in a 250 mL round bottom flask. 50 mL of ethanol was addedand the mixture was refluxed for 16 h. Celite was added to the cooledsolution and the mixture was poured onto a 2 inch bed of silica gel. Thesilica bed was then washed twice with ethanol (2×100 mL), followed byhexanes (2×100 mL). The product was then eluted through the silica plugwith dichloromethane. Most of the dichloromethane was removed undervacuum and the product was precipitated with 2-propanol and filtered,washed with hexanes and dried to give 1.67 g of product (52.8% yield).

Example 19 Synthesis of Compound 23

Synthesis of 2,5-diphenyl-6-methylpyridine

Phenylboronic acid (24.3 g, 199.25 mmol), 2,5-dibromo-6-methypyridine(10 g, 39.85 mmol), 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (654mg, 1.5 mmol), and potassium phosphate tribasic (27.5 g, 119.5 mmol),300 mL of toluene and 30 mL of water were placed in a 1 L round-bottomflask. Nitrogen was bubbled directly into the mixture for 30 min afterwhich tris(dibenzylideneacetone)dipalladium(0) (364 mg, 0.398 mmol) wasadded. Nitrogen was bubbled for another 15 min then the reaction mixturewas heated to reflux for 16 h under nitrogen. After the reaction wascompleted, the mixture was cooled and the organic layer was separated.The organic layer was washed with a saturated brine solution and driedover magnesium sulfate. The solution was filtered and the solventremoved under vacuum. The crude was purified by column chromatographyusing silica gel as the stationary phase and 10%-20% ethyl acetate inhexanes as the mobile phase. 9.0 g of desired product was obtained afterpurification (92.7% yield)

Synthesis of Ir Dimer

IrCl₃.3H₂O (1.6 g, 4.66 mmol) and 2,5-diphenyl-6-methylpyridine (4.0 g,16.31 mmol) was placed in a 250 mL round bottomed flask. 45 mL of2-ethoxyethanol and 15 mL of water were added. The mixture was refluxedunder nitrogen for 16 h. The reaction mixture was then allowed to coolto room temperature. The precipitate was filtered and washed withmethanol followed by hexanes. After drying, 2.75 g of dimer was obtained(84.6% yield).

Synthesis of Ir Triflate

The iridium dimer (2.75 g, 2.2 mmol) was dissolved in 200 mL ofdichloromethane. Silver triflate (1.19 g, 4.6 mmol) was dissolved in 100mL of methanol and added to the iridium dimer solution. The resultingmixture was stirred for 5 h. The solution was then passed through acelite plug to remove silver chloride. The solvent was evaporated undervacuum to give 3.5 g of the iridium triflate. The solid was used fornext step without further purification.

Synthesis of Compound 23

The iridium triflate (3.0 g) and 2,5-diphenyl-6-methylpyridine (3.0 g)was placed in a 100 mL round bottom flask. The solid mixture was heatedto 130° C. for 16 h. After cooling the reaction mixture was dissolved in200 mL of dichloromethane. The solution was then passed through a 2 inchsilica gel plug. The solvent was removed under vacuum and the residuewas chromatographed using silica gel with dichloromethane as the mobilephase. Most of the solvent was evaporated and the product wasprecipitated with 2-propanol and filtered, washed with hexanes and thendried to give 2.65 g of product (71% yield).

Example 20 Synthesis of Compound 24

Synthesis of 2,5-(m-tolyl)-4-methylpyridine

m-tolylboronic ester (17.9 g, 132 mmol), 2,5-dibromo-4-methypyridine(11.0 g, 44.0 mmol), 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl(726 mg, 1.77 mmol), and potassium phosphate tribasic monohydrate (30 g,130 mmol), 143 mL of toluene and 33 mL of water were placed in a 500 mLround-bottom flask. Nitrogen was bubbled directly into the mixture for30 min after which tris(dibenzylideneacetone)dipalladium(0) (394 mg, 43mmol) was added. Nitrogen was bubbled for another 15 min then thereaction mixture was heated to reflux for 16 h under nitrogen. Themixture was allowed to cool to room temperature and the organic layerwas separated from the aqueous layer. The organic layer was washed witha saturated brine solution and dried over magnesium sulfate. Thesolution was filtered and the solvent removed under vacuum to give anoff white product. The crude was purified by column chromatography usingsilica gel as the stationary phase and 10% ethyl acetate in hexanes asthe mobile phase. 11.2 g of desired product was obtained afterpurification. (93.3% yield)

Synthesis of Ir Dimer

IrCl₃.3H₂O (1.8 g, 4.86 mmol) and 2,5-ditolyl-4-methylpyridine (4.0 g,14.6 mmol) was placed in a 100 mL round bottomed flask. 24 mL of2-ethoxyethanol and 8 mL of water were added. The mixture was refluxedunder nitrogen atmosphere for 16 h. The reaction mixture was thenallowed to cool to room temperature. The precipitate was filtered andwashed with methanol followed by hexanes. After drying, 3.0 g of theiridium dimer was obtained (79.6% yield).

Synthesis of Ir Triflate

3.0 g of the iridium dimer was dissolved in 380 mL of dichloromethane.Silver triflate (1.0 g, 4.08 mmol) was dissolved in 20 mL of isopropanoland added to the iridium dimer solution. The resulting mixture wasstirred for 5 h. The solution was then poured through a celite plug toremove silver chloride. The solvent was evaporated under vacuum to give2.7 g of the iridium triflate. The solid was used for next step withoutfurther purification.

Synthesis of Compound 24

The iridium triflate (2.7 g, 2.95 mmol) and (3.6 g, 13.2 mmol) of2,5-ditolyl-4-methylpyridine was placed in a 250 mL round bottom flask.100 mL of ethanol was added and the mixture was refluxed for 16 h.Celite was added to the cooled solution and the mixture was poured ontoa 2 inch bed of silica gel. The silica bed was then washed twice withethanol (2×50 mL), followed by hexanes (2×50 mL). The product was theneluted through the silica plug with dichloromethane. Most of thedichloromethane was removed under vacuum and the product wasprecipitated with 2-propanol and filtered, washed with hexanes and driedto give 2.4 g of product (80.6% yield).

Example 21 Synthesis of Compound 25

Synthesis of 2-phenyl-5-(m-tolyl)pyridine

2-methylphenyl boronic acid (5.1 g, 37.59 mmol),2-phenyl-5-bromopyridine (8.0 g, 34.17 mmol),2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (561 mg, 1.366 mmol),and potassium phosphate tribasic (23.50 g, 102.51 mmol), 250 mL oftoluene and 25 mL of water were placed in a 1 L round-bottom flask.Nitrogen was bubbled directly into the mixture for 30 min after whichtris(dibenzylideneacetone)dipalladium(0) (312 mg, 0.341 mmol) was added.Nitrogen was then bubbled for another 15 minutes and the reactionmixture was heated to reflux for 16 h under nitrogen. The mixture wascooled and the organic layer was separated from the aqueous layer. Theorganic layer was washed with saturated brine solution, dried overmagnesium sulfate, filtered, and the solvent removed under vacuum togive an off-white solid as the crude. The crude was purified by columnchromatography using silica gel as the stationary phase and 2% ethylacetate in hexanes as the mobile phase. 6.5 g of desired product wasobtained after purification (78% yield).

Synthesis of Compound 25

The iridium triflate (from the synthesis of compound 1) (3.25 g) and2-phenyl-5-tolylpyridine (3.2 g) were placed in a 250 mL round bottomflask. A 50:50 mixture of methanol and ethanol (100 mL) was added andthe mixture was refluxed for 16 h. Celite was added to the cooledsolution and the mixture was poured onto a 2 inch bed of silica gel. Thesilica bed was then washed twice with ethanol (2×100 mL), followed byhexanes (2×100 mL). The product was then eluted through the silica plugwith dichloromethane. The dichloromethane was removed under vacuum togive the crude product as a mixture of compounds. The desired compoundwas separated and isolated by column chromatography using silica gel asthe stationary phase and 1:1 dichloromethane/hexanes as the mobilephase. 0.53 g of desired product was obtained after purification (15.6%yield).

Example 22 Synthesis of Compound 26

Synthesis of Compound 26

The iridium triflate (3.25 g) and 2-phenyl-5-tolylpyridine (3.2 g) wereplaced in a 250 mL round bottom flask. A 50:50 mixture of methanol andethanol (100 mL) was added and the mixture was refluxed for 16 h. Celitewas added to the cooled solution and the mixture was poured onto a 2inch bed of silica gel. The silica bed was then washed twice withethanol (2×100 mL), followed by hexanes (2×100 mL). The product was theneluted through the silica plug with dichloromethane. The dichloromethanewas removed under vacuum to give the crude product as the desiredcompound. The compound was further purified by column chromatographyusing silica gel as the stationary phase and 1:1 dichloromethane/hexanesas the mobile phase. 3.38 g of desired product was obtained afterpurification (100% yield).

Example 23 Synthesis of Compound 27

Synthesis of 2-phenyl-4-chloropyridine

2,4-dichloropyridine (10 g, 67.57 mmol), phenylboronic acid (9.0 g,74.32 mmol), and potassium carbonate (28 g, 202.70 mmol), 300 mLdimethoxyethane and 30 mL of water was placed in a 1 L round-bottomflask. Nitrogen was bubbled directly into the mixture for 30 min.Tetrakis(triphenylphosphine)palladium(0) (780 mg, 0.675 mmol) was addedand nitrogen was bubbled into the reaction mixture for a another 15 min.The reaction mixture was then heated to reflux under nitrogen for 16 h.The reaction was then allowed to cool to room temperature and dilutedwith ethyl acetate and water. The organic and aqueous layers wereseparated and the aqueous layer was extracted with ethyl acetate. Theorganic layers were combined and washed with a saturated brine solution.The organic layer was then dried over magnesium sulfate, filtered, andthe solvent was removed under vacuum to give an off-white solid ascrude. The crude was purified by column chromatography using silica gelas the stationary phase and 2% ethyl acetate in hexanes as the mobilephase. 8.0 g of desired product was obtained after purification (54%yield). 11.5 g of desired product was obtained after purification(89.77% yield).

Synthesis of 2-phenyl-4-(m-tolyl)pyridine

2-methylphenyl boronic acid (6.3 g, 46.40 mmol),2-phenyl-4-chloropyridine (8.0 g, 42.18 mmol),2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (692 mg, 1.68 mmol), andpotassium phosphate tribasic (29.10 g, 126.54 mmol) 250 mL of tolueneand 25 mL of water were placed in a 500 mL round-bottom flask. Nitrogenwas bubbled directly into the mixture for 30 min after whichtris(dibenzylideneacetone)dipalladium(0) (386 mg, 0.421 mmol) was added.Nitrogen was then bubbled for another 15 minutes then the reactionmixture was heated to reflux for 16 h under nitrogen. The mixture wascooled and the organic layer was separated from the aqueous layer. Theorganic layer was washed with a saturated brine solution, dried overmagnesium sulfate, filtered, and the solvent removed under vacuum togive an off-white solid as the crude. The crude was purified by columnchromatography using silica gel as the stationary phase and 2% ethylacetate in hexanes as the mobile phase. 8.0 g of desired product wasobtained after purification (77.4% yield).

Synthesis of Compound 27

The iridium triflate (4.0 g) and 2-phenyl-4-o-tolylpyridine (4.0 g) wereplaced in a 250 mL round bottom flask. A 50:50 mixture of methanol andethanol (100 mL) was added and the mixture was refluxed for 16 h. Celitewas added to the cooled solution and the mixture was poured onto a 2inch bed of silica gel. The silica bed was then washed twice withethanol (2×100 mL), followed by hexanes (2×100 mL). The product was theneluted through the silica plug with dichloromethane. The dichloromethanewas removed under vacuum to give the crude product as a mixture ofcompounds. The desired compound was separated and isolated by columnchromatography using silica gel as the stationary phase and 1:1dichloromethane/hexanes as the mobile phase. 2.0 g of desired productwas obtained after purification (48% yield).

Example 24 Synthesis of Compound 28

Synthesis of Compound 28

The iridium triflate (4.0 g) and 2-phenyl-4-o-tolylpyridine (4.0 g) wasplaced in a 250 mL round bottom flask. A 50:50 mixture of methanol andethanol (100 mL) was added and the mixture was refluxed for 16 h. Celitewas added to the cooled solution and the mixture was poured onto a 2inch bed of silica gel. The silica bed was then washed twice withethanol (2×100 mL), followed by hexanes (2×100 mL). The product was theneluted through the silica plug with dichloromethane. The dichloromethanewas removed under vacuum to give the crude product as the desiredcompound. The compound was further purified by column chromatographyusing silica gel as the stationary phase and 1:1 dichloromethane/hexanesas the mobile phase. 3.6 g of desired product was obtained afterpurification (86.6% yield).

Example 25 Synthesis of Compound 29

Synthesis of Compound 29

The iridium triflate (4.0 g, 4.62 mmol) and (2.15 g, 13.87 mmol) of2-phenylpyridine were placed in a 100 mL round-bottom flask. A 50:50mixture of methanol and ethanol (60 mL) was added and the mixture wasrefluxed for 16 h. Celite was added to the cooled solution and themixture was poured onto a 2 inch bed of silica gel. The silica bed wasthen washed twice with ethanol (2×50 mL), followed by hexanes (2×50 mL).The product was then eluted through the silica plug withdichloromethane. The dichloromethane was removed under vacuum to givethe crude product as a mixture of compounds. The desired compound wasseparated and isolated by column chromatography using silica gel as thestationary phase and 1:1 dichloromethane/hexanes as the mobile phase.1.1 g of desired product was obtained after purification (31.6% yield).

Example 26 Synthesis of Compound 30

Synthesis of Compound 30

The iridium triflate (3.2 g) and 2,5-diphenyl-4-ethylpyridine (3.2 g)was placed in a 250 mL round bottom flask. 50 mL of ethanol was addedand the mixture was refluxed for 16 h. Celite was added to the cooledsolution and the mixture was poured onto a 2 inch bed of silica gel. Thesilica bed was then washed twice with ethanol (2×50 mL), followed byhexanes (2×50 mL). The product was then eluted through the silica plugwith dichloromethane. The dichloromethane was removed under vacuum togive the crude product as a mixture of compounds. The desired compoundwas separated and isolated by column chromatography using silica gel asthe stationary phase and 1:1 dichloromethane/hexanes as the mobilephase. 1.22 g of desired product was obtained after purification (31.6%yield).

Example 27 Synthesis of Compound 31

Synthesis of 2-phenyl-5-methylpyridine

2-bromo-5-methylpyridine (11.25 g, 65.39 mmol), phenylboronic acid (9.5g, 78.47 mmol), 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (1.0 g,2.61 mmol), and potassium phosphate tribasic (45 g, 196.17 mmol), 250 mLof toluene and 25 mL of water were placed in a 500 mL round-bottomflask. Nitrogen was bubbled directly into the mixture for 30 min afterwhich tris(dibenzylideneacetone) dipalladium(0) (598 mg, 0.653 mmol) wasadded. Nitrogen was bubbled for another 15 min then the reaction mixturewas heated to reflux for 16 h under nitrogen. The mixture was cooled andthe organic layer was separated from the aqueous layer. The organiclayers are washed with saturated brine solution, dried over magnesiumsulfate, filtered, and the solvent removed under vacuum to give anoff-white solid as the crude. The crude was purified by columnchromatography using silica gel as the stationary phase and 5%-10% ethylacetate in hexanes as the mobile phase. 10.11 g of desired product wasobtained after purification (92% yield).

Synthesis of Ir Dimer

2-phenyl-5-methylpyridine (10.11 g, 59.8 mmol) and IrCl₃.3H₂O (6.0 g, 17mmol) were dissolved in 90 mL of 2-ethoxyethanol and 30 mL of water in a250 mL round-bottom flask. The reaction mixture was refluxed undernitrogen for 16 h. The reaction mixture was then allowed to cool to roomtemperature and the precipitate was filtered and washed with methanolfollowed by hexanes. The iridium dimer was then dried under vacuum andused for the next step without further purification. 8.75 g of the dimerwas obtained after vacuum drying (91.0% yield).

Synthesis of Ir Triflate

The iridium dimer (8.74 g, 7.75 mmol) was dissolved in 1.0 L ofdichloromethane. Silver triflate (4.18 g, 16.27 mmol) was dissolved in500 mL of methanol and added to the iridium dimer solution. Theresulting mixture was stirred for 18 h. The solution was then passedthrough a celite plug to remove silver chloride and the solvent wasevaporated to give 4.0 g of iridium triflate. The solid was used fornext step without further purification.

Synthesis of Compound 31

The iridium triflate (4.0 g) and 2,5-diphenyl-4-methylpyridine (4.0 g)were placed in a 250 mL round bottom flask. A 50:50 mixture of methanoland ethanol (80 mL) was added and the mixture was refluxed for 16 h.Celite was added to the cooled solution and the mixture was poured ontoa 2 inch bed of silica gel. The silica bed was then washed twice withethanol (2×100 mL), followed by hexanes (2×100 mL). The product was theneluted through the silica plug with dichloromethane. The dichloromethanewas removed under vacuum to give the crude product as a mixture ofcompounds. The desired compound was separated and isolated by columnchromatography using silica gel as the stationary phase and 1:1dichloromethane/hexanes as the mobile phase. 3.75 g of desired productwas obtained after purification (90% yield).

Example 28 Synthesis of Compound 32

Synthesis of Compound 32

The iridium triflate (2.6 g, 3.66 mmol) and 2,5-ditolyl-4-methylpyridine(3.0 g, 11 mmol) were placed in a 100 mL round bottom flask. A 50:50mixture of methanol and ethanol (50 mL) was added and the mixture wasrefluxed for 16 h. Celite was added to the cooled solution and themixture was poured onto a 2 inch bed of silica gel. The silica bed wasthen washed twice with ethanol (2×100 mL), followed by hexanes (2×100mL). The product was then eluted through the silica plug withdichloromethane. The dichloromethane was removed under vacuum to givethe crude product as a mixture of compounds. The desired compound wasseparated and isolated by column chromatography using silica gel as thestationary phase and 1:1 dichloromethane/hexanes as the mobile phase.0.9 g of desired product was obtained after purification (31.8% yield).

Example 29 Synthesis of Compound 33

Synthesis of Compound 33

The iridium triflate (2.8 g) and 2-phenylpyridine (2.8 g) were placed ina 250 mL round bottom flask. A 50:50 mixture of methanol and ethanol (80mL) was added and the mixture was refluxed for 16 h. Celite was added tothe cooled solution and the mixture was poured onto a 2 inch bed ofsilica gel. The silica bed was then washed twice with ethanol (2×100mL), followed by hexanes (2×100 mL). The product was then eluted throughthe silica plug with dichloromethane. The dichloromethane was removedunder vacuum to give the crude product as the desired compound. Thecompound was further purified by column chromatography using silica gelas the stationary phase and 1:1 dichloromethane/hexanes as the mobilephase. 2.3 g of desired product was obtained after purification (73.2%yield).

Example 30 Synthesis of Compound 34

Synthesis of Compound 34

The iridium triflate (3.5 g) and 2-phenyl-5-methylpyridine (3.5 g) wereplaced in a 250 mL round bottom flask. A 50:50 mixture of methanol andethanol (80 mL) was added and the mixture was refluxed for 16 h. Celitewas added to the cooled solution and the mixture was poured onto a 2inch bed of silica gel. The silica bed was then washed twice withethanol (2×100 mL), followed by hexanes (2×100 mL). The product was theneluted through the silica plug with dichloromethane. The dichloromethanewas removed under vacuum to give the crude product as a mixture ofcompounds. The desired compound was separated and isolated by columnchromatography using silica gel as the stationary phase and 1:1dichloromethane/hexanes as the mobile phase. 1.25 g of desired productwas obtained after purification (31.4% yield).

Example 31 Synthesis of Compound 35

Synthesis of Compound 35

2-phenyl-5-o-tolylpyridine (8.8 g, 35.9 mmol, 6 eq) and Iridium trisacetylacetonate (2.93 g, 5.98 mmol, 1 eq) were placed in a 50 mLround-bottom flask. The flask was purged with nitrogen for 0.5 h. Thereaction mixture was then heated to 230° C. in a sand bath for 48 h. Thereaction mixture was allowed to cool to room temperature and 100 mL ofdichloromethane was added. The mixtures was filtered through a silicagel plug. The solvent was removed under vacuum to give the crudeproduct. The crude was purified by column chromatography using silicagel as the stationary phase and 1:1 dichloromethane/hexanes as themobile phase. 0.4 g of desired product was obtained after purification(7.2% yield).

Example 32 Synthesis of Compound 36

Synthesis of Compound 36

The iridium triflate and 3 molar equivalent of 2-phenylpyridine can bedissolved in a 50:50 mixture of methanol and ethanol and the mixturerefluxed for 16 h. The mixture can be purified using a method similar tothat described in Example 30.

Example 33 Synthesis of Compound 37

Synthesis of Compound 37

The iridium triflate (2.45 g) and 2,5-diphenyl-4-ethylpyridine (2.58 g)was placed in a 250 mL round bottom flask. 50 mL of ethanol was addedand the mixture was refluxed for 16 h. Celite was added to the cooledsolution and the mixture was poured onto a 2 inch bed of silica gel. Thesilica bed was then washed twice with ethanol (2×50 mL), followed byhexanes (2×50 mL). The product was then eluted through the silica plugwith dichloromethane. The dichloromethane was removed under vacuum togive the desired compound. The compound was further purified by columnchromatography using silica gel as the stationary phase and 1:1dichloromethane/hexanes as the mobile phase. 1.25 g of desired productwas obtained after purification (48% yield).

Device Examples

All device examples were fabricated by high vacuum (<10⁻⁷ Torr) thermalevaporation. The anode electrode is 1200 Å of indium tin oxide (ITO).The cathode consisted of 10 Å of LiF followed by 1000 Å of Al. Alldevices were encapsulated with a glass lid sealed with an epoxy resin ina nitrogen glove box (<1 ppm of H₂O and O₂) immediately afterfabrication, and a moisture getter was incorporated inside the package.

The organic stack of the Device Examples 1 and 2 in Table 2, consistedof sequentially, from the ITO surface, 100 Å of E1 as the hole injectionlayer (HIL), 300 Å of 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl(α-NPD) as the hole transporting later (HTL), 300 Å of H1 doped with 7%or 10% of Compound 1 as the emissive layer (EML), 50 Å of H1 as theblocking layer, and 400 Å of Alq₃ (tris-8-hydroxyquinoline aluminum) asthe ETL. The device structure of the Device Examples is also summarizedin FIG. 3.

Comparative Examples 1 and 2 were fabricated similarly to the DeviceExamples, except that E1 was used as the emissive dopant.

The device structures and data are summarized in Table 2 and Table 3.Table 2 shows device structure, and Table 3 shows the correspondingmeasured results for those devices. As used herein, E1, H1 and NPD, havethe following structures:

TABLE 2 Device Example HIL HTL Host Dopant % BL ETL 1 E1 NPD H1 Compound1 H1 50 Å Alq₃ 100 Å 300 Å  7% 450 Å Comparative E1 NPD H1 E1 7% H1 50 ÅAlq₃ Example 1 100 Å 300 Å 450 Å 2 E1 NPD H1 Compound 1 H1 50 Å Alq₃ 100Å 300 Å 10% 450 Å Comparative E1 NPD H1 E1 10% H1 50 Å Alq₃ Example 2100 Å 300 Å 450 Å

TABLE 3 At 1000 cd/m² At J = 40 mA/cm² λ_(max) CIE V LE EQE PE LoRT_(80%) RT_(50%) Ex. (nm) X Y (V) (cd/A) (%) (Im/W) (cd/m²⁾ (hr) (hr) 1558 0.440 0.546 6.2 64.4 19.2 32.6 18,504 265  900 Comp. Ex. 1 528 0.3550.607 6 53.4 14.7 27.9 15,985 214  760 2 560 0.449 0.537 6 59.5 18.231.1 19,320 400 1400 Comp. Ex. 2 529 0.357 0.607 5.9 53.2 14.6 28.316,781 340 1130

From the Device Examples in Table 3, it can be seen that devicescontaining the inventive compound may have particularly good properties.Specifically, devices having an emissive layer containing Compound 1 asthe emissive dopant. These devices demonstrate that Compound 1 may bebeneficial to device stability. In particular, Comparative Example 1 andDevice Example 1 have RT_(80%) (defined as the time taken for theinitial luminance, L₀, to drop to 80% of its initial luminance) of 760and 900 h, respectively. Comparative Example 2 and Device Example 2 haveRT_(80%) of 1130 and 1400 h, respectively. These results indicate thatextended conjugation of heteroleptic Ir (III) complexes may bebeneficial to device stability.

Low evaporation temperature is desirable for OLED manufacturing.Prolonged heating of the materials is required during OLEDmanufacturing, so materials having a low evaporation temperature haveless thermal stress typically resulting in cleaner evaporations. Theextended conjugation achieved by adding a phenyl to the heteroatomicring of Compound 1 results in a low sublimation temperature. Therefore,devices with Compound 1 may have improved manufacturing.

The organic stack of the Device Examples 3-12 in Table 4, consisted ofsequentially, from the ITO surface, 100 Å of E1 as the hole injectionlayer (HIL), 300 Å of 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl(α-NPD) as the hole transporting later (HTL), 300 Å of H1 or H2 dopedwith 7%, 10% or 15% of an invention compound as the emissive layer(EML), 50 Å of H1 or H2 as the blocking layer, and 400 Å of Alq₃(tris-8-hydroxyquinoline aluminum) as the ETL. The device structure ofthe Device Examples is also summarized in FIG. 3.

Comparative Example 3 was fabricated similarly to the Device Examples,except that E1 was used as the emissive dopant.

The device structures and data are summarized in Table 4 and Table 5.Table 4 shows device structure, and Table 5 shows the correspondingmeasured results for those devices. As used herein, E1, H1, H2 and NPD,have the following structures:

TABLE 4 Device Example HIL HTL Host Dopant % BL ETL Example 1 E1 NPD H1Compound 1 H1 Alq₃ 450 Å 100 Å 300 Å  7%  50 Å Example 2 E1 NPD H1Compound 1 H1 Alq₃ 450 Å 100 Å 300 Å 10%  50 Å Example 3 E1 NPD H2Compound 2 H2 Alq₃ 400 Å 100 Å 300 Å  7% 100 Å Example 4 E1 NPD H2Compound 2 H2 Alq₃ 400 Å 100 Å 300 Å 10% 100 Å Example 5 E1 NPD H2Compound 8 H2 Alq₃ 400 Å 100 Å 300 Å  7% 100 Å Example 6 E1 NPD H2Compound 8 H2 Alq₃ 400 Å 100 Å 300 Å 10% 100 Å Example 7 E1 NPD H2Compound 9 H2 Alq₃ 400 Å 100 Å 300 Å  7% 100 Å Example 8 E1 NPD H2Compound 9 H2 Alq₃ 400 Å 100 Å 300 Å 10% 100 Å Example 9 E1 NPD H2Compound 10 H2 Alq₃ 400 Å 100 Å 300 Å  7% 100 Å Example 10 E1 NPD H2Compound 10 H2 Alq₃ 400 Å 100 Å 300 Å 10% 100 Å Example 11 E1 NPD H2Compound 11 H2 Alq₃ 400 Å 100 Å 300 Å  7% 100 Å Example 12 E1 NPD H2Compound 11 H2 Alq₃ 400 Å 100 Å 300 Å 10% 100 Å Example 13 E1 NPD H2Compound 12 H2 Alq₃ 400 Å 100 Å 300 Å  7% 100 Å Example 14 E1 NPD H2Compound 12 H2 Alq₃ 400 Å 100 Å 300 Å 10% 100 Å Example 15 E1 NPD H2Compound 12 H2 Alq₃ 400 Å 100 Å 300 Å 15% 100 Å Comparative E1 NPD H1 E17% H1 Alq₃ 450 Å Example 1 100 Å 300 Å  50 Å Comparative E1 NPD H1 E110% H1 Alq₃ 450 Å Example 2 100 Å 300 Å  50 Å Comparative E1 NPD H2 E17% H2 Alq₃ 400 Å example 3 100 Å 300 Å 100 Å

TABLE 5 CIE At 1000 cd/m² At J = 40 mA/cm² λ max, V LE EQE PE Lo,RT_(80%), RT_(50%), Ex. nm X Y (V) (cd/A) (%) (lm/W) (cd/m²) (hr) (hr)Ex. 1 558 0.440 0.546 6.2 64.4 19.2 32.6  8,504 265  900 Ex. 2 560 0.4490.537 6 59.5 18.2 31.1 19,320 400 1400 Ex. 3 543 0.417 0.569 6 70.5 19.636.9 19,818 390 Ex. 4 545 0.426 0.562 5.3 65.5 18.4 38.8 20,393 480 Ex.5 536 0.383 0.594 6.4 48.8 13.3 24.1 14,056 440 Ex. 6 537 0.388 0.5906.4 42.4 11.6 20.9 13,158 440 Ex. 7 532 0.367 0.602 6.3 51.4 14.1 25.614,637 305 Ex. 8 533 0.37 0.602 6 42.7 11.7 22.5 13,031 340 Ex. 9 5320.376 0.598 5.7 59.2 16.3 32.6 16,212 225 Ex. 10 533 0.378 0.597 5.258.2 16 35.1 17,151 240 Ex. 11 541 0.411 0.575 5.5 73.7 20.3 42.2 21,430335 Ex. 12 545 0.420 0.568 4.9 76 21.1 48.6 24,136 480 Ex. 13 525 0.3420.612 5.8 56.9 15.8 30.7 15,843 208 Ex. 14 527 0.337 0.619 5 62.9 17.239.5 18,952 330 Ex. 15 528 0.349 0.611 5 55.7 15.3 34.8 17,941 320 Comp.528 0.355 0.607 6 53.4 14.7 27.9 15,985 214  760 Ex. 1 Comp. 529 0.3570.607 5.9 53.2 14.6 28.3 16,781 340 1130 Ex. 2 Comp. 528 0.361 0.601 6.552.1 14.6 25.2 14,768 250 Ex. 3

From the Device Examples in Table 4, it can be seen that devicescontaining the inventive compound may have particularly good properties.Specifically, devices having an emissive later containing Compound 1,Compound 2, Compound 8-12 as the emissive dopant demonstrate that theseinventive compounds may be beneficial to device stability.

Particular devices are provided wherein inventive compounds, Compound 21through Compound 35, are the emitting dopant and H-2 is the host. Theorganic stack of the Device Examples 21-35 consisted of sequentially,from the ITO surface, 100 Å of E1 as the hole injection layer (HIL), 300Å of 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (α-NPD) as the holetransporting later (HTL), 300 Å of H2 doped with 7% of Compound 21-35and 37 as the emissive layer (EML), 100 Å of H2 as the electrontransporting layer (ETL2), and 400 Å of Alq₃ (tris-8-hydroxyquinolinealuminum) as the electron transporting layer (ETL1).

Comparative Device Examples 4-6 were fabricated similarly to the DeviceExamples, except E2 was used the emitting dopant in Comparative DeviceExample 4; CBP was as the host, E3 was used as the emitting dopant, and50 Å of HPT was used as the ETL2 and 450 Å of Alq₃ was used as the ETL1in Comparative Device Example 5; in E4 was used as the emitting dopantin Comparative Device Example 6.

As used herein, the following compounds have the following structures:

Particular materials for use in an OLED are provided. The materials maybe used an emitting dopant in the emissive layer of such a device. Thematerials provided herein may be used to provide devices having highefficiency and a narrow electroluminescence. In addition, thesematerials may provided improved stability and improved processibility,such as high solubility and low evaporation temperature.

TABLE 6 Evaporation temperature Device Example Compound (° C.) Example16 21 239 Example 17 22 232 Example 18 23 250 Example 19 25 216 Example20 26 202 Example 21 27 205 Example 22 28 208 Example 23 29 204 Example24 30 203 Example 25 31 213 Example 26 32 209 Example 27 34 236 Example28 35 216 Example 29 37 202 Comparative example 4 E2 230 Comparativeexample 5 E3 270 Comparative example 6 E4 204

Table 6 shows the evaporation temperature of the emitting compounds,Compounds 21-33, used in the Device Examples compared to the evaporationtemperatures of the emitting compounds E2 and E3 used in ComparativeDevice Examples 4 and 5, respectively. In particular, Compounds 21-24have significantly lower evaporation temperatures than E3. A lowerevaporation temperature may be a desirable property for the thermalevaporation and long term thermal stability of dopants. It is believedthat the C-ring phenyl-pyridine in Compounds 21-23 has more twistbetween the two rings than the phenyl-pyridine twist, as is present inE3. The heteroleptic compounds (Compounds 25-33 and 37) which containthe twisted C-ring feature have similar or lower evaporationtemperatures than E2 which does not have a C-ring at all. The resultindicates that the twisted C-ring feature may lower evaporationtemperature while keeping the molecular weight as high or even higherthan the structurally similar compounds without this feature.

TABLE 7 CIE λ_(max) FWHM Device Example (nm) (nm) x y Example 16 526 680.337 0.623 Example 17 528 64 0.342 0.622 Example 18 520 66 0.324 0.622Example 27 532 68 0.368 0.607 Comparative example 4 519 74 0.321 0.621Comparative example 5 548 70 0.43 0.56 Comparative example 6 520 740.320 0.632

Table 7 shows additional device data for Device Examples and ComparativeExamples. In particular, Table 7 provides λ_(max) and CIE coordinatesfor Device Examples 16-18 and 27 compared to the Comparative DeviceExamples 4, 5 and 6. From the data, it can be seen that Device Examples16-18 and 27 are significantly blue shifted from Comparative DeviceExample 5. This result suggests that the conjugation may be reduced bythe presence of the twisted phenyl C-ring.

TABLE 8 At J = 40 CIE At 1000 cd/m² mA/cm² FWHM V LE EQE PE LE L_(o)RT_(80%) Ex. λ_(max) (nm) x y (V) (cd/A) (%) (lm/W) EQE (cd/m²) (h) 16526 68 0.337 0.623 6.9 49.3 13.3 22.4 3.7 16,895 210 17 528 64 0.3420.622 6.0 55.1 14.8 28.7 3.7 18,175 260 18 520 66 0.324 0.622 6.9 43.712.0 19.9 3.6 16,240  54 19 532 72 0.372 0.599 5.4 65.6 17.8 38.0 3.718,482 245 20 532 70 0.36 0.608 5.6 69 18.6 39 3.7 19,934 142 21 538 820.371 0.594 5.8 59.8 16.6 32.2 3.6 17,658 174 22 532 74 0.346 0.613 7.159.7 16.2 26.5 3.7 14,187  90 23 528 70 0.345 0.616 5.4 62.5 17 36.5 3.719,280 237 24 522 70 0.327 0.623 5.4 63.3 17.3 36.7 3.7 18,212 223 25528 70 0.342 0.618 5.2 66.6 18.1 40.5 3.7 19,280 254 26 532 74 0.3690.600 5.9 59.7 16.3 31.6 3.7 16,240  42 27 532 72 0.361 0.608 4.9 59.616.0 43.2 3.7 20,057 290 28 532 68 0.368 0.607 5.2 67.6 18 40.6 3.820,324 200 29 522 72 0.333 0.619 5.6 62.7 17.2 35.0 3.6 17,205 121 Comp.519 74 0.321 0.621 6 45.1 12.6 23.6 3.6 13,835 196  4 Comp. 520 74 0.3200.632 5.5 54.9 14.9 31.2 3.7 17,153  42  6

Table 8 provides a comparison of device properties between DeviceExamples 16-29 and Comparative Examples 4 and 6. From the data, it canbe seen that Device Examples 16 (Compound 21), 17 (Compound 22), 19(Compound 25), 20 (Compound 26), 21 (Compound 27), 23 (Compound 29), 24(Compound 30), 25 (Compound 31), 27 (Compound 34), 28 (Compound 25), 29(Compound 37) provide high efficiency and long device lifetime.Particularly, Device Examples 16, 17, 19, 23, 24, 25 and 27, which useCompounds 21, 22, 25, 29, 30, 31 and 34 respectively as the emittingdopant, have very good device performance. These particular devices showan RT_(80%) (defined as the time required for the initial luminance L₀to drop to from 100% to 80% at room temperature under constant DC drive)of 210, 260, 245 237, 223, 254 and 290 h compared to an RT_(80%) of 196h of Comparative Device Example 4. Furthermore, Device Examples 16, 17,19, 23, 24, 25 and 27 all operate at higher L₀ than Comparative DeviceExample 4. The result indicates that the phenyl C-ring may improve thedevice stability by adding some conjugation to emitting dopant. However,the conjugation is limited by the presence of the twist feature,described above, which does not cause significant red-shift in emissioncompared to a phenyl in regular conjugation as in E-3. In addition, theEL spectra of Device Examples 16-20, 23-25 and 27-29 are all narrowerthan that of Comparative Example 4. Narrow emission may be an desirablefactor for achieving saturated color coordinates, high LE:EQEconversion, microcavity tuning, and color filter matching in OLEDtechnology.

It is understood that the various embodiments described herein are byway of example only, and are not intended to limit the scope of theinvention. For example, many of the materials and structures describedherein may be substituted with other materials and structures withoutdeviating from the spirit of the invention. The present invention asclaimed may therefore includes variations from the particular examplesand preferred embodiments described herein, as will be apparent to oneof skill in the art. It is understood that various theories as to whythe invention works are not intended to be limiting.

The invention claimed is:
 1. A compound comprising a ligand L having the structure:

wherein B and C are each independently a 5 or 6-membered carbocyclic or heterocyclic ring; wherein A-B represents a bonded pair of carbocyclic or heterocyclic rings coordinated to a metal M via a nitrogen atom in ring A and an sp² hybridized atom in ring B; wherein A-C represents a bonded pair of carbocyclic or heterocyclic rings; wherein R_(a), R_(b), and R_(c) may represent mono, di, tri, or tetra substitutions; wherein R_(a), R_(b), and R_(c) are independently selected from the group consisting of hydrogen, alkyl, alkoxy, amino, alkenyl, alkynyl, arylkyl, aryl, and heteroaryl; wherein X₁, X₂, X₃, X₄, X₅, X₆, X₇, X₈, and X₉ are independently selected from carbon and nitrogen; wherein R₁ and R₂ are independently selected from the group consisting of hydrogen, alkyl, alkoxy, amino, alkenyl, alkynyl, arylkyl, aryl, and heteroaryl; and wherein at least one of R₁, R₂, and the R_(a) substituents adjacent to C is not hydrogen; wherein the ligand L is coordinated to a metal M having an atomic number greater than 40; and wherein A is pyridine.
 2. The compound of claim 1, wherein only one of R₁, R₂, and the R_(a) substituents is not hydrogen.
 3. The compound of claim 1, wherein only one of R₁, R₂, and the R_(a) substituents is alkyl.
 4. The compound of claim 1, wherein only one of R₁, R₂, and the R_(a) substituents is ethyl.
 5. The compound of claim 1, wherein only one of R₁, R₂, and the R_(a) substituents is methyl.
 6. The compound of claim 1, wherein the compound has the structure:

wherein m is the oxidation state of the metal M; wherein n is at least 1; wherein L′ is a monoanionic bidentate ligand.
 7. The compound of claim 6, wherein the metal M is Ir.
 8. The compound of claim 6, wherein only one of R₁, R₂, and the R_(a) substituents adjacent to C is not hydrogen.
 9. The compound of claim 6, wherein only one of R₁, R₂, and the R_(a) substituents adjacent to C is alkyl.
 10. The compound of claim 6, wherein only one of R₁, R₂, and the R_(a) substituents adjacent to C is ethyl.
 11. The compound of claim 6, wherein only one of R₁, R₂, and the R_(a) substituents adjacent to C is methyl.
 12. The compound of claim 6, wherein the compound is selected from the group consisting of:

wherein R is not hydrogen.
 13. The compound of claim 12, wherein R is an alkyl.
 14. The compound of claim 13, wherein the compound is selected from the group consisting of:


15. The compound of claim 9, wherein the alkyl is on the pyridine ring.
 16. The compound of claim 9, wherein the alkyl is para to the nitrogen of the pyridine ring.
 17. An organic light emitting device, comprising: an anode: a cathode; and an organic layer, disposed between the anode and the cathode, the organic layer further comprising a compound having the formula:

wherein B and C are each independently a 5 or 6-membered carbocyclic or heterocyclic ring; wherein A-B represents a bonded pair of carbocyclic or heterocyclic rings coordinated to the metal M via a nitrogen atom in ring A and an sp² hybridized atom in ring B; wherein A-C represents a bonded pair of carbocyclic or heterocyclic rings; wherein R_(a), R_(b), and R_(c) may represent mono, di, tri, or tetra substitutions; wherein R_(a), R_(b), and R_(c) are independently selected from the group consisting of hydrogen, alkyl, alkoxy, amino, alkenyl, alkynyl, arylkyl, aryl, and heteroaryl; wherein X₁, X₂, X₃, X₄, X₅, X₆, X₇, X₈, and X₉ are independently selected from carbon and nitrogen; wherein R₁ and R₂ are independently selected from the group consisting of hydrogen, alkyl, alkoxy, amino, alkenyl, alkynyl, arylkyl, aryl, and heteroaryl; and wherein at least one of R₁, R₂, and the R_(a) substituents adjacent to C is not hydrogen; and wherein the ligand L is coordinated to a metal having an atomic number greater than 40; and wherein A is pyridine.
 18. A heteroleptic complex having the formula Ir(L_(A-B))₂(L_(C-D)), wherein L_(A-B) is

wherein L_(C-D) is selected from the group consisting of

and wherein R₁, R₂, R₃, R₄ and R₅ are each independently selected from the group consisting of hydrogen and alkyl; wherein each of R₁, R₂, R₃, R₄ and R₅ may represent mono, di, tri, tetra, or penta substitutions; and wherein R₁, R₂, R₃, R₄ and R₅ are each independently selected from hydrogen and methyl.
 19. The compound of claim 18, wherein L_(C-D) is selected from the group consisting of:


20. The compound of claim 18, wherein the compound is: 